THE  WILEY  AGRICULTURAL  ENGINEERING  SERIES 


EDITED    BY 


J.  B.  DAVIDSON,  A.E. 

Professor  of  Agricultural  Engineering.  Iowa  State  College 


HIGHWAY  ENGINEEKING 

RURAL   ROADS 
AND  PAVEMENTS 


BY 

GEORGE  R.  CHATBURN,  A.M.,  C.E. 

Professor  of  Applied  Mechanics  and  Machine  Design 

and   Lecturer  on   Highway   Engineering 

The  University  of  Nebraska,  Lincoln 


NEW  YORK 

JOHN  WILEY  -&  SONS,  INC. 

LONDON:  CHAPMAN  &  HALL,  LIMITED 

1921 


COPYRIGHT,  1921 
BY  GEORGE  R.  CHATBURN 


PRESS  OF 

BRAUNWORTH    &   CO. 

BOOK  MANUFACTURERS 

BROOKLYN,   N.  V. 


PREFACE 


IN  writing  a  text-book  on  a  subject  which  is  growing  as 
rapidly  as  highway  engineering  is  at  the  present  time  one  finds 
himself  confronted  with  a  varying  practice.  The  student  who 
desires  the  latest  up-to-date  matter  on  roads  must  consult 
contemporaneous  engineering  periodicals  and  literature  and  sift 
from  them  what  he  deems  best  suited  to  his  purpose.  In  this 
work  the  author  has  endeavored  to  bring  into  a  brief  space  the 
most  recent  and  best  practice  as  determined  by  his  experience 
and  research. 

As  this  text  is  more  especially  concerned  with  rural  roads, 
those  types  of  roads  most  common  in  the  rural  districts,  small 
cities,  and  towns,  or  best  adapted  for  use  therein,  have  been 
covered  in  greatest  detail.  Pavements  have  been  treated 
largely  with  a  view  to  their  use  for  country  roads,  although  the 
treatment  is  thought  to  be  sufficiently  comprehensive  to  form 
a  beginning  or  short  course  for  those  desirous  of  taking  up  city 
paving  work.  The  author  is  of  the  opinion  that  almost  all  of 
the  principles  of  road  building  applicable  to  rural  highways 
are  equally  applicable  to  city  streets  and  vice  versa. 

While  technical  analyses  and  technical  language  have  not 
been  shunned,  it  has  been  constantly  borne  in  mind  that  the 
book  is  intended  primarily  to  form  one  of  a  series  in  agricultural 
education.  It  is  believed,  therefore,  that  the  work  is  of  such  a 
character  that  it  will  be  read  with  interest  by  the  layman  and, 
because  here  are  brought  together  many  ideas  from  many 
sources,  will  serve  as  a  useful  reference  book  for  professional 
engineers,  road  builders,  and  road  officers. 

A  method  of  calculating  mixtures  to  conform  to  the  Fuller 
maximum  density  curve  for  concrete,  the  New  York  sheet 

iii 


iv  PREFACE 

asphalt  mixture,  or  any  other  selected  or  predetermined  sieve 
analysis  design,  is  given.  This,  as  far  as  the  author  knows, 
is  original  and,  he  thinks,  mathematically  correct  and  rigid, 
avoiding  much  of  the  guesswork  of  the  older  presentations. 
He  has  also  illustrated  his  straight-line  method  for  plotting 
granulometric  analyses,  which  seems  to  have  advantages  over 
the  ordinary  method.  Tentative  methods  for  testing  sand- 
clay  mixtures  are  included;  these,  while  not  yet  standardized 
by  technical  organizations,  are  in  daily  practical  use.  A 
graded  mixture  for  gravel  roads  based  upon  the  maximum 
density  curve  is  suggested.  The  surveying  and  location  of 
roads  has  been  gone  into  with  considerable  detail,  because  with 
the  present  inability  of  the  railways  to  serve  the  public  ade- 
quately the  author  looks  for  increased  business  by  motor  trans- 
port and  consequently  greater  interest  to  be  manifested  in 
constructing  new  lines  of  highway  and  straightening  and 
shortening  old. 

In  the  preparation  of  the  text,  naturally  many  sources 
have  been  consulted.  Throughout,  references  have  been  sub- 
tended ;  if  any  have  been  overlooked  it  has  been  unintentional. 
However,  those  sources  most  freely  consulted  are  here  men- 
tioned : 

Periodicals: 

11  Engineering  and  Contracting." 

"  Engineering  Record  "  1  ,,  ^     .        .      XT 

tt^     .  „      \"  Engineering  News-Record." 

"  Engineering  News  " 

"  Good  Roads." 

Highway  Engineering  Text-books: 
Baker's  "  Roads  and  Pavements." 

Blanchard  and  Browne's  "  Text-book  on  Highway  Engi- 
neering." 

Blanchard's  "  Highway  Engineers'  Handbook." 
Harger  and  Bonney's  "  Handbook  for  Highway  Engineers." 
Richardson's  "  Modern  Asphalt  Pavements." 
Richardson's  "  Asphalt  Construction." 
Hubbard's  "  Dust  Prevention  and  Road  Binders." 


PREFACE  V 

HubbarcTs  "  Highway  Inspectors'  Handbook." 
Spalding's  "  Text-book  on  Roads  and  Pavements." 
Tillson's  "  Street  Pavements  and  Paving  Materials." 
Frost's  "  Art  of  Road  Making." 
Judson's  "  City  Roads  and  Pavements." 

Publications  of  Engineering  and  Other  Technical  Societies: 
American  Society  for  Testing  Materials. 
American  Society  of  Civil  Engineers. 
American  Society  for  Municipal  Improvements. 
American  Road  Builders'  Association. 
National  Paving  Brick  Manufacturers'  Association. 
National  Conference  on  Concrete  Road  Building. 
National  Highways  Association. 
Portland  Cement  Association. 

National  and  State  Publications: 

Office  of  Public  Roads  and  Rural  Engineering,  United  States 

Department  of  Agriculture. 
Bureau  of  Standards,  United  States  Deprtment  of  Commerce 

and  Labor. 
Many  State  Highway  Departments  and  Reports  of  Highway 

Engineers. 

Other  Engineering  and  Technical  Text-books: 

Taylor  and  Thompson's  "  Concrete,  Plain  and  Reinforced." 

Hool's  "  Reinforced  Concrete  Construction." 

Turneaure  and  Maurer's  "  Principles  of  Reinforced  Concrete 

Construction." 

Johnson's  "  Materials  of  Construction."   „ 
Mills'  "  Materials  of  Construction." 
Benson's  "  Industrial  Chemistry." 
Middleton's  "  Building  Materials." 

Wellington's  "  Economic  Theory  of  the  Location  of  Rail- 
ways." 

Lavis'  "  Railroad  Location." 
Pence  and  Ketcham's  "  Surveying  Manual." 
Nagle's  "  Field  Manual  for  Railroad  Engineers." 
Merriman's  "  American  Civil  Engineers'  Pocket  Book." 


Vi  PREFACE 

Abraham's  "  Asphalts  and  Allied  Substances." 
Ries  and  Watson's  "  Engineering  Geology." 

Commercial  Literature: 

The  bulletins    and    catalogues   of   manufacturers   of   road 
materials  and  road  machinery. 

To  the  authors  and  publishers  of  all  the  sources  used  the 
author's  sincere  thanks  are  due,  as  well  as  to  Professor  C.  E. 
Mickey  and  other  associates  in  the  University  of  Nebraska. 

GEORGE  R.  CHATBURN. 
LINCOLN,  NEBRASKA, 
September,  1920 


TABLE  OF  CONTENTS 


CHAPTER  I 
INTRODUCTION 

PAGE 

Good  roads  a  business  proposition — Chief  value  of  good  roads — Eco- 
nomic advantages  of  good  roads — Effect  on  the  business  man — 
Overhead  charges  reduced — Primary  and  secondary  transporta- 
tion denned — Cost  of  hauling — Amount  of  haulage — Traffic  cen- 
DUS  —  Traffic  area  —  Tonnage  —  Economic  investment  —  Farm 
trucks  and  motor  transport — Maintenance  costs — Summary.  .  .  1 

CHAPTER  II 
ROAD  LOCATION 

An  engineering  problem — General  principles  of  road  location — Direct- 
ness— Grades — Fise  and  fall — Minimum  grade — Laying  out  the 
road — Reconnoissance — Preliminary  survey — Stationing — Stakes 
— Grades  or  gradient — Party  organization — Operation  of  taking 
preliminary  traverse  —  Transit  man  —  Head  chainman  —  Rear 
chainman — Stake  man — Axman — Front  flagman — Rear  flagman 
— Level  party — Operation  of  level — Rodman — Topographer — 
Draftsman — Plotting — Profile — Establishing  grade  line — Earth- 
work computation — Crown  correction — Location — Curves — 
Simple  curve  formulas — Laying  out  the  curve — With  transit — 
By  chord  offsets — By  tangent  offsets — Striking  in — By  eye — 
Parabolic  curves — vertical  curves — Adjustment  of  the  transit  and 
level — Important  adjustments — The  plate  bubble — Line  of  colli- 
mation  —  The  standards  —  Attached  level  —  Y-level —  Line  of 
collimation — Level  viol — The  Y's — Dumpy  level — Bubble — 
Line  of  collimation — Cross-sectioning — Defined — Cross-sections — 
Slope  stakes — Grade  stake — Grade  point — Leveling — With  hand 
level — With  level  board — with  Y-level — Grade  stakes — Setting 
stakes — Slope  states — Cross-section  notes — Calculating  quantities 
— Rules  for  calculating  cross-sectional  areas — Miscellaneous — 
Crown — Blade  grader  work — Shrinkage  settlement — Borrow  pits 


viii  TABLE  OF  CONTENTS 


— Wasted  earth — Existing  road  layouts — Relocations  along 
existing  lines — The  party — Surveying  operations — Office  work- 
Field  procedure 19 

CHAPTER  III 
TYPES  AND  ADAPTATION  OF  ROADS 

Points  to  be  considered — Types  of  roads — Earth — Sand  clay— Gravel 
— Macadam — Bituminous  macadam — Brick — Concrete — Asphalt 
Blocks— Sheet  asphalt— Plank— Coal  slack— Shell— Furnace  slag- 
Cinders — Wheelways — Burned  clay — Corduroy — Hay — Compari- 
son of  roads 79 

CHAPTER  IV 
DRAINAGE 

Surface  drainage — Crown — Methods  for  calculating  and  staking  out — 
Side  ditches — Guard  rails — Sub-drainage — Deep  side  ditches — 
Blind  drains — Drain  tile — Size  of  tile — Laying  the  tile — Tools — 
Filling  the  ditch — Outlet  and  inlet  protection — V-drains — 
Draining  ponds — Water  courses — Resume 87 

CHAPTER   V 
CULVERTS  AND  BRIDGES 

Definitions — Size  of  waterway — Design  of  bridge  or  culvert — Tem- 
porary and  emergency  structures — Wooden  box  culverts — High- 
water  low  bridge — Pile  and  stringer  bridge — More  permanent 
structures — Cast-iron — Corrugated  iron  and  steel  plate — Outlet 
and  protection — Vitrified  clay  pipe — Standards  for  strength — • 
Cement  pipe — Twin  pipe  culvert — End  protection — Intake 
drop — Box-culverts — Method  of  construction — Wooden  forms — 
Deposition  of  concrete — Removal  of  forms — Head  and  wing  walls 
— Slab  bridges — Arch  culverts — Forms — Removing  forms — Fords .  .  103 

CHAPTER  VI 
EARTH  ROADS 

Definition — Clay; — Sand — Drainage — Width — Clearing — Staking  out 
— Width  and  cross-section  of  roadway — Formula  and  dimensions 
— Grading — Definitions — Grading  machines  and  tools — Blade 
grader — Harrow — Plow — Drag  or  slip  scraper — Tongue  scraper 


TABLE  OF  CONTENTS  ix 

PAGE 

Fresno  or  Buck  scraper — Wheel  scrapers — Dump  wagons — Ele- 
vating grader — Spades  and  shovels,  picks,  axes,  brush  hooks,  corn 
knife — Steam  shovels,  drag-line  scrapers,  industrial  railways — 
Borrowed  earth  and  borrow  pits — Embankment — Haul  and  over- 
haul— Shrinkage — Tractors  vs.  horses — Maintenance — Periodic 
and  continuous — Dragging — Drags — Theory  of  dragging — Method 
of  using  the  drag — Patrol  system  of  maintenance — Duties  of 
patrolmen 123 

CHAPTER  VII 
SAND-CLAY  ROADS 

Theory  of — Selection  of  materials — Sampling— Separation  of  sand 
and  clay — Mechanical  analysis  of  sand — Standard  sand-clay 
mixtures — Plotting  sieve  analyses — Method  of  proportioning — 
Other  tests — Slaking  test — Koch's-James'  Field  test — Flouring 
test — Test  for  mica  and  feldspar — Construction  of  sand-clay  roads — 
Sanded  roads — Clayed  roads — Top-soil  roads — Maintenance — 
Cost 150 

CHAPTER  VIII 

GRAVEL  ROADS 

Definitions — Density  curves — Mechanical  analyses  curves  defined — 
Sieves — Calibrating  sieves — Suggested  grading  for  gravel — Great 
refinement  in  grading  not  necessary — Specifications  for  road 
gravel — Adopting  and  plotting  the  standard  grading — Selecting 
gravel — Chemical  tests — Binding  action  of  gravel — Construction — 
Drainage — Design — Surface  method — Trench  method — Chert  or 
flint — Repairs  and  maintenance 167 

CHAPTER  IX 
BROKEN-STOME  ROADS 

Testing  road  stone  —  Hardness — Toughness  —  Cementing  value  — 
Abrasion  test — Specific  gravity — Apparent  specific  gravity — 
Absorption — Compression — Simple  Methods  of  judging  rock  char- 
acter— Weathering — Hammer  tests — Classification  of  rocks — Igne- 
ous rocks — Sedimentary  rocks — Metamorphic  rocks — Mineral 
composition — Principal  road  rocks — Trap — Basalt — Diabase — 
Peridotite — Andesite — Diorites — Granites — Syenites — Gneisses — 
Construction  of  stone  roads — Subgrade — Telford  and  Macadam — 


TABLE   OF  CONTENTS 


Subgrade— Cross-sections— Courses— Placing  the  stone — Upper 
course — Shoulders— Width  and  thickness  of  macadam — Main- 
tenance— Continuous  method — Periodic  method — Effect  of  auto- 
mobile on  macadam — Crushers  and  screens 181 

CHAPTER  X 

PAVEMENT  FOUNDATIONS 

Definition  and  purpose — Subgrade — Safe  bearing  loads — Strengthen- 
ing the  sub-grade— Foundations  proper— Telford  stone  founda- 
tion— Missouri — Macadam — V-drain — Hydraulic  Concrete — Con- 
crete defined — Methods  of  proportioning — Measuring  aggregates 
— Hand  mixing — Machine  mixing — Placing — Protection  during 
hardening — The  aggregate — Coarse  aggregate — Organic  matter 
detrimental — Fine  aggregate — Concrete  manufactured  in  place — 
Concrete  slabs — Bituminous  concrete  foundations — Brick  foun- 
dations   202 

CHAPTER  XI 
BRICK,  STONE,  WOOD,  AND  OTHER  BLOCK  ROADS 

Block  roads  defined — Brick  roads — Vitrified  paving  brick — Manufac- 
ture— Testing  paving  brick — Rattler  test — Standard  rattler — 
Average  losses — Visual  inspection — Design  and  construction  of 
brick  roads— -Subgrade  and  drainage — Curbing — Foundation — 
Concrete  foundation — Brick  foundation — Sand  cushion — Laying 
the  brick — Rolling — Expansion  joints — Filler — Portland  cement 
grout  filler — Illinois  specification — Bituminous  filler — Specifica- 
tions— Pouring — Paint  coat — Monolithic  brick  pavement — Bed- 
ding method — Cement-sand  method — Direct  method — Green 
cement  method — Inspecting  and  rolling — Maintenance — Stone 
block  pavements — Dimensions  of  blocks — Physical  properties — 
Varieties  of  material  used — Specifications — Construction — Small 
and  recut  blocks — Wood  block  pavement — Wood,  varieties  used 
— Preparation— Treatment — Tests — Laying — Filling — Expansion 
joints — Bituminized  brick 211 

CHAPTER  XII 

CONCRETE  ROADS 

Description  and  definition — Materials — Cement — Specifications  and 
tests — Aggregates — Fine  aggregate — Qualifications — Granulomet- 
ric  analysis — Graded  sand — Coarse  aggregate — Qualifications — 
Water — Reinforcement — Proportioning  concrete — By  arbitrary  se- 


TABLE  OF  CONTENTS  xi 

PAGE 

lection — By  voids — Errors — Proportioning  by  maximum  density 
theory — Illustrative  examples — Mathematical  theory — Abram's 
fineness  modulus  method  of  proportioning  and  designing  concrete 
mixtures — Proportions  used  in  practice — Proportioning  the  very 
fine  aggregate — Quantities  of  materials — Fuller's  rule — Taylor 
and  Thompson's  rule — Illustrative  examples — Mixing  the  con- 
crete— Mixers — Rotary — Paddle — Gravity— Measuring  the  mate- 
rials— Automatic  devices — Measuring  barrows — Weighing  devices 
— Consistency — Bureau  of  Standards  definitions — Slump  test  for — 
Cylinder — Truncated  cone — Quantity  of  water — Abram's  rule — 
Duration  and  speed  of  mixing — Placing  the  concrete — Striking  off 
templates — Joining  straight  edge — Forms — Finishing — Floats, 
belts — Roller — Wood  tamping  templates — Reinforcing — Curing 
and  protection — Ponding — Two-course  work — Expansion  and  con- 
traction joints — Joint  protection  plates — Cross-section — Thick- 
ness—Width— Crown— Integral  curb — Maintenance — Filling  cracks 
— More  extensive  repairs — Seal  coat  or  carpet — Cost  of  concrete 
roads — Grouted  concrete — Oil-cement  concrete — Organization — 
Planning  beforehand — Selecting  the  mixer — Handling  materials . . '  233 

CHAPTER  XIII 
BITUMINOUS  ROADS 

Defined — Materials — Classification — Definitions — Sources  of  bitu- 
minous  materials — Native  asphalts — Petroleum  asphalts — Road 
tars  and  pitches — Physical  and  chemical  tests — Consistency  test — 
Penetration  method — Viscosimeter  method — New  York  Testing 
Laboratory  float  test — Melting-point — Cube  method — Ring  and 
ball  method — Solubility  tests — Test  for  fixed  carbon — Bituminous 
earth  roads — Oiled  earth  roads — Bituminized  earth  roads — Bitu- 
minized sand  roads — Layer  method  of  construction — Bituminized 
gravel  roads — Bituminous  broken-stone  roads — Bituminous  mac- 
adam— Drainage  and  foundation — Mineral  aggregate — Specifica- 
tions for  bituminous  cement — Construction — Subgrade — Wearing 
surface — Crusher  run  stone — Uniform  stone — Partially  filled 
voids — Mechanically  mixed  filler — Sand-cement  mastic  layer — 
Seal  coat  —  Maintenance  —  Bituminous  concrete  —  Definition  — 
Classification  —  Patented  mixtures  —  Materials  —  Stone — Bitu- 
minous cement  —  Proportioning  —  Construction — Foundation — 
Mixing — Temperature  of  mixing— Laying — Rolling — Seal  coat — 
Maintenance  —  Sheet  A  sphalt— Definition — Foundation — Binder 
course — Open — Closed — Wearing  course — Typical  specifications 
— Mineral  aggregate — Filler — Complete  topping  mixture  design — 
Construction — Maintenance— Rock  asphalt — Asphalt  blocks 289 


xii  TABLE  OF   CONTENTS 

CHAPTER  XIV 
SURFACE  TREATMENT  TO  MITIGATE  AND  PREVENT  DUST 

PAGE 

Cause  of  dust — Palliatives  and  preventives — Defined — Palliatives — • 
Water — Sea  water — Oil  and  water — Deliquescent  salts — Emul- 
sions— Organic  substances — Light  oils — Tars — Animal  and  vege- 
table oils — Preventives — Classification — Materials — Specifications 
—Oiled  roads— Construction— Oil 322 

CHAPTER  XV 
REVENUE  ADMINISTRATION  AND  ORGANIZATION 

Revenue  —  Taxes  —  Direct  —  Property  —  Special  —  Labor  —  General 
— Indirect  taxation  —  Bonds — Sinking-fund — Serial — Annuity — 
Comparison — Licenses — Administration — Development  of  road 
systems — Foreign — United  States — Constitutional  provision — 
Lancaster  turnpike — Cumberland  road — Later  developments — 
State  aid — History — State  Highway  Departments — How  made 
up — Powers — State  highway  laws — Roads  classified — State  high- 
way commissioners — State  highway  engineer — Typical  laws — One 
person  commission — I.Iultiple-person  commission — Duties  of  high- 
way departments — Miscellaneous  —  Educational — State  road — 
— Co-operative — Organization  charts — national  and  state — County 
and  township  organizations 333 

CHAPTER  XVI 

MISCELLANEOUS 

Road  signs  and  emblems — Route  marks,  direction  signs,  danger  signs — 
Metal  and  concrete — Detour  signs — Rules  for — Placing — Road 
maintenance  competition — Score  card  for  road  maintenance  con- 
tests— Rating  local  road  superintendents — Race  tracks 356 


HIGHWAY  ENGINEERING 

CHAPTER  I 

INTRODUCTION 

GOOD  ROADS  A  BUSINESS  PROPOSITION 

THE  business  transactions  of  the  world  are  measured  in 
money,  but  no  medium  of  exchange  can  measure  many  of  the 
most  valuable  things  mankind  enjoys — for  example,  good 
health,  fresh  air,  the  education  obtained  in  the  common  schools, 
the  roads  traveled  upon.  Poor  health  is  a  direct  source  of  ex- 
pense and  indirectly  the  cause  of  great  money  losses.  Men  have 
given  thousands  of  dollars  to  prevent  the  erection  of  buildings 
which  would  cut  off  their  supply  of  sunlight  and  fresh  air. 
The  lack  of  an  education  is  so  great  a  handicap  to  the  individual 
and  so  detrimental  to  the  welfare  of  the  nation  that  the  greatest 
of  all  taxes  are  those  paid  to  keep  up  the  schools.  Bad  roads 
are  stagnation  and  even  death  to  trade  and  commerce,  resulting 
in  large  losses  of  time  and  money.  The  great  blessings  that 
come  with  the  enjoyment  of  these  things  and  the  serious  dis- 
advantages and  losses  of  their  absence  are  fully  realized;  yet, 
due  to  the  lack  of  knowledge  of  intimate  relationships  existing 
between  the  various  interests  of  life,  a  definite  value  in  dollars 
and  cents  cannot  be  placed  upon  any  one  of  these  useful  and 
necessary  elements.  Local  conditions,  individual  differences, 
sentiment,  supply  and  demand,  and  many  other  factors  must 
enter  into  an  estimate  of  what  a  thing  is  worth.  But,  not- 
withstanding this,  many  efforts  have  been  made  by  road 
economists  to  evaluate  the  benefits  derived  from  good  and 


2  GOOD  ROAbS  A  BUSINESS  PROPOSITION 

the  losses  due  to  bad  rbacls.  Several  years  ago  the  United 
States  Office  of  Public  Roads  published  a  bulletin  in  which 
an  effort  was  made  to  show  that  the  cost  of  hauling  on  the 
country  roads  was  annually  about  $900,000,000;  and  that 
with  uniformly  good  roads  there  might  be  a  saving  of  more 
than  $600,000,000.  Professor  L.  W.  Chase  makes  a  very 
plausible  calculation  to  show  that  the  average  farmer  in 
Nebraska  would  save  each  year  $147  if  the  road  leading  from 
his  farm  to  his  market  were  dragged  after  each  rain.  Interesting 
and  instructive  as  such  claculations  are,  they  are  nevertheless 
futile  because  uniformly  good  roads  would  themselves  change 
other  conditions  and  affect  markets. 

The  chief  value  of  good  roads  is  not  in  the  actual  money 
saving  they  produce,  but  they  are  desirable  for  the  same  reason 
that  a  man  buys  a  carriage  or  a  carpet;  they  appeal  to  his 
desire  for  comfort,  for  beauty,  for  pleasure,  for  style.  In  the 
early  days  the  pioneers  lived  in  log,  in  sod,  or  other  makeshift 
houses;  people  could  do  so  to-day  if  they  wished.  A  man 
could  go  to  church  or  to  a  polite  function  wearing  overalls 
and  jumper,  but  he  prefers  other  styles  of  clothing.  In  a 
great  many  things  economic  factors  are  of  minor  importance. 
Nevertheless,  it  is  worth  while  to  consider  some  of  the 

ECONOMIC  ADVANTAGES  OF  GOOD  ROADS 

Good  roads  decrease  the  cost  of  transportation  by  allowing 
larger  loads  to  be  hauled  or  by  saving  in  time. 

Good  roads  save  in  the  wear  and  tear  of  wagons,  harness, 
horse-flesh,  automobiles,  trucks  and  tractors. 

Good  roads  and  the  possibility  of  daily  marketing  allow 
the  cultivation  of  crops  not  otherwise  profitable — of  intensive 
farming.  Whole  families  have  been  known  to  support  them- 
selves upon  small  patches  of  5  or  10  acres  by  gardening. 
Other  crops  would  require  40  acres  and  still  others  160 
acres.  As  a  rule,  the  smaller  the  number  of  acres  required 
to  support  a  family  the  more  perishable  the  crop  raised  and 
the  consequent  greater  need  for  good  roads  and  quick  market- 
ing. The  same  rule  applies  to  mercantile  pursuits.  .Novelties 


ECONOMIC  ADVANTAGES  OF  GOOD  ROADS      3 

that  are  perishable  or  liable  to  go  out  of  style  and  be  left  on 
the  merchant's  shelves  bring  the  greatest  nominal  profit,  while 
the  staple  article  that  is  good  year  after  year  is  handled  upon 
the  smallest  margin.  The  safer  the  investment  the  smaller  the 
interest  charges.  Still,  few  large  fortunes  are  made  without 
assuming  some  risk.  Occasionally,  fruit  crops  bring  $500  per 
acre;  strawberries,  melons,  tomatoes,  like  high  returns.  Ordi- 
narily with  such  crops  the  risk  is  great.  Early  frosts,  insects, 
drought,  glutted  markets,  and  bad  roads  may  cut  down  the 
profits.  The  safer  such  crops  can  be  made  by  improved  roads 
and  stable  markets  the  more  intensive  farming  will  be  ex- 
tended. The  rural  districts,  due  to  the  combining  of  farms 
brought  about  by  the  use  of  improved  machinery  and  manage- 
ment and  the  prosperity  of  the  farmers,  are  decreasing  in 
population.  Make  it  profitable  to  diversify  farming  and  raise 
the  more  perishable  crops  and  instead  of  farms  growing  larger 
and  the  rural  population  smaller,  the  farms  will  become  smaller 
and  the  population  larger. 

Good  roads  give  a  wider  choice  in  the  time  of  marketing. 
This,  in  connection  with  the  feasibility,  due  to  good  roads, 
of  the  rural  delivery  of  mails,  making  it  possible  for  the  pro- 
ducer, through  his  daily  paper,  to  keep  in  touch  with  the 
markets  and  take  advantage  of  high  prices,  may  mean  con- 
siderable to  the  farmer  in  the  course  of  a  year.1 

Effect  on  the  Business  Man  of  the  Town. — Savings  in 

1  This  increase  of  the  value  of  (farm  lands  reached  by  rural  delivery) 
has  been  estimated  as  high  as  $5  per  acre  in  some  states.  A  moderate 
estimate  is  from  $2  to  $3  per  acre.  In  the  Western  States  especially  the 
construction  of  good  roads  has  been  a  prerequisite  of  the  establishment 
of  rural  free  delivery  service.  Better  prices  are  obtained  for  farm 
products,  the  producers  being  brought  into  daily  touch  with  the  state  of 
the  markets,  and  thus  being  enabled  to  take  advantage  of  information 
heretofore  unattainable.  To  these  material  advantages  may  be  added 
the  educational  advantages  conferred  by  relieving  the  monotony  of  farm 
life  through  ready  access  to  wholesome  literature  and  the  keeping  of  all 
rural  residents,  the  young  people  as  well  as  their  elders,  fully  informed 
as  to  the  stirring  events  of  the  day.  The  moral  value  of  these  civilizing 
influences  cannot  be  too  highly  rated. — Report  of  the  U.  S.  Postmaster 
General. 


4  GOOD  ROADS  A  BUSINESS  PROPOSITION 

transportation  will  be  more  or  less  equitably  distributed  among 
the  producer,  middleman  and  ultimate  consumer.  Each 
will  receive  a  portion.  But  suppose  the  whole  or  major  part 
remained  with  the  producer.  As  his  profits  increased  so  would 
his  expenditures;  he  would  buy  lumber,  nails, .  and  other 
materials,  to  build  larger  and  better  barns  and  houses.  He 
would  install  the  modern  conveniences:  water,  light,  heat,  and 
sanitary  equipment;  he  would  buy  a  new  range  for  the  kitchen, 
a  new  carpet  for  the  floor,  new  furniture  for  the  parlor,  china 
and  silver  for  the  table/ a  piano  for  the  daughter,  a  gold  watch 
for  the  son,  and  an  automobile  for  the  whole  family.  A  general 
increase  in  the  prosperity  of  several  members  of  a  community 
is  bound  to  make  itself  felt  throughout  the  entire  community. 

Merchants  want  trade ;  they  spend  money  advertising  for  it. 
But  what  good  is  advertising  when  the  roads  are  impassable  or 
even  with  difficulty  traversable.  Usually  the  poorest  roads 
are  just  on  the  edge  of  town,  where  a  large  volume  of  traffic 
converges,  and  just  as  a  chain  is  no  stronger  than  its  weakest 
link,  so  a  road  with  a  single  bad  place  may  divert  much  trade 
from  a  community.  But  every  good  road  leading  to  town  is  a 
hand  stretched  out  to  welcome  and  invite  trade. 

Good  Roads  Reduce  Overhead  Charges. — Because  market- 
ing of  crops  must  be  confined  to  periods  of  good  roads,  there  is  at 
such  seasons  a  glut  in  the  market  and  a  consequent  reduction  in 
prices  paid  the  producer,  but  usually  no  corresponding  reduc- 
tion to  the  consumer.  Warehouses  and  elevators  have  to  be 
built  larger  than  would  be  necessary  were  roads  uniformly  good 
the  whole  year  round.  A  greater  number  of  railroad  cars 
must  be  provided  to  take  care  of  the  congested  traffic,  only  to 
lie  idle  on  side  tracks  in  seasons  of  bad  roads.  Interest  and 
overhead  charges  upon  these  extra  buildings  and  equipment 
must  eventually  be  paid  by  the  producer,  the  middleman,  and 
the  consumer,  reducing  the  profits  of  the  first  and  second  and 
increasing  the  expenses  of  the  third.  This  depression  is  reflected 
and  all  commercial  and  financial  interests  are  affected.  The 
United  States  is  said  to  be  "  handicapped  in  all  the  markets  of 
the  world  by  an  enormous  waste  of  labor  in  the  primary  trans- 


, 
PRIMARY  AND  SECONDARY  TRANSPORTATION          5 

portation  of  our  products  and  manufactures,  while  our  home 
markets  are  restricted  by  difficulties  in  rural  distribution  which 
not  infrequently  clog  all  the  channels  of  transportation,  trade, 
and  finance." 

Primary  Transportation  is  a  term  applied  to  transportation 
on  a  public  highway  whether  it  be  of  raw  products  to  market  or 
of  finished  products  to  the  consumer.  Transportation  by  rail- 
roads, canals,  and  ships  may  be  denominated  as  secondary. 
Practically  all  secondary  transportation  is  of  products  which 
were  first  or  last  or  both  the  subjects  of  primary  transportation. 
The  Department  of  Statistics  of  the  U.  S.  Government  has 
studied 1  the  production  and  marketing  of  twelve  leading 
products.  These  twelve  amount  to  85|  billion  pounds  (42.7 
million  tons)  per  annum.  All  this  must  be  transported  pri- 
marily and  much  of  it  secondarily  at  a  cost  roughly  2  estimated 
as  follows: 

1.  By  wagons  and  horses:  CTon*ufT 

1.  On  poor  earth  roads 50 

2.  On  good  earth  roads 20 

3.  On  macadamized  roads 11 

4.  On  paved  streets 6 

2.  By  trolley  cars: 

1.  On  steel  track .  . .  . , 2 

2.  Trackless  paved  roadway 5 

3.  By  automobile  or  motto  truck: 

1.  Individual  (not  busy  all  time) 8 

2.  Co-operative  (busy  all  the  time) ....     5 

4.  By  steam  or  gasoline  tractor: 

1.  Over  earth  roads,  medium  condition.  12 

2.  Over  earth  roads,  best  condition ....     8 

5.  By  steam  railroad  3 f 

1  U.  S.  Dept.  of  Agriculture,  Bulletin  No.  49,  "  Cost  of  hauling  crops," 
by  Frank  Andrews. 

2  It  must  be  remembered  that  no  one  knows  the  exact  cost  of  primary 
transportation.     It  varies  with  constantly  varying  conditions. 

3  Secondary  transportation.     Average  of  all  products.     See  reports  of 
U.  S.  Railway  Commission. 


6  GOOD  ROADS  A  BUSINESS  PROPOSITION 

To  go  a  little  more  into  detail,  from  the  same  government  bul- 
letin it  is  ascertained  that  during  the  year  1905-6  the 

Pounds  of  wheat  hauled  were 24,246,000,000 

Value $302,261,000 

Cost  of  hauling  100  Ibs 9  cents 

Cost  of  hauling  total $21,821,400 

Per  cent  of  value 7.2 

This  may  be  looked  at  from  another  angle : 

Cost  of  hauling  wheat  to  market  9.4  mi.  per  100  Ib .  .  .  9  cents 
Cost  of  hauling  same  wheat  from  Omaha  to  New 

York  per  100  Ib 25.7  cents 

Cost  of  getting  to  railroad         9         1 
Cost  of  gettingto  seaboard  =23j  =  m==apprOXUnately  *' 

Or,  the  cost  to  a  farmer  in  the  Middle  West  of  getting  his 
wheat  to  the  railroad  is  one-third  the  cost  of  getting  it  from  his 
railroad  station  to  the  seaboard. 

Again,  the  cost  of  hauling  wheat  on  wagon  roads  per 

100  Ib.  per  mile  is  about 1    cent 

The  cost  of  hauling  it  on  the  railroad  per  mile  is -/$  cent 

A  ONE-CENT  POSTAGE  STAMP  WILL  PAY  FOR  TRANSPORT- 
ING 100  POUNDS  OF  WHEAT 


With  horses  on  a  poor  earth  road \  mi. 

With  horses  on  a  good  earth  road 1  mi. 

With  horses  on  a  macadamized  road.  ...      2  mi. 

With  horses  on  a  paved  road 3  mi. 

With  a  tractor  on  a  good  earth  road 3  mi. 

With  a  trolley  on  a  paved  road 4  mi. 

With  a  motor  truck  on  a  good  earth  road      6  mi. 

With  a  trolley  on  steel  track 10  mi. 

With  a  steam  or  electric  locomotive  on  a 

steel  track 25  mi. 

With  an  ocean-going  steamship 200  mi. 

With  an  ocean-going  sailing  vessel 400  mi. 


FIG.  1. — Cost  of  Transportation 


COST  OF  TRANSPORTATION 


Very  roughly,  then,  a  one-cent  postage  stamp  will  pay  for  trans- 
porting 100  Ib.  of  wheat  the  distances  shown  in  Fig.  I.1 

All  this  goes  to  show  that  our  rural  road  transportation  is 
the  most  expensive  and  that  any  material  saving  in  this  item 
will,  either  directly  or  indirectly,  greatly  benefit  all  classes  of 
people. 

1  The  costs  given  in  Fig.  1  were  compiled  before  the  War.  They  are 
Jiow  probably  too  low.  Babson's  Bulletin  for  February,  1919,  gives  the 
costs  of  hauling  corn  in  nine  widely  separated  localities  from  23  to  52  cents 
per  ton  mile,  average  39;  by  motor  trucks  from  11  to  36  cents,  with  an 
average  of  18. 

The  Motor  Truck  Association  of  America  compiled  the  costs  shown 
below  for  the  operation  of  trucks  in  large  fleets  such  as  are  employed  by 
interurban  haulage  companies: 

MOTOR  TRUCK  COST  PER  DAY  FOR  FIVE-TON  GASOLINE  UNIT  BASED 

ON  50  MILES  PER  DAY  PER  TRUCK  AND  300  DAYS  PER  YEAR 

TAKEN   FROM   THE   RECORDS   FOR   SIX   TRUCKS 

Direct  Charges 


A 
Amt. 

B 
Amt. 

C 

Amt. 

D 
Amt. 

E 
Amt. 

F 
Amt. 

Average 

Amt. 

Total 

Driver  
Tires 

$5.00 
3.00 
3  00 

$5.20 
3.75 

$5.00 
2.00 
.30 
3.50 

$5.00 
2.00 
.50 
4.65 

$5.17 
2.00 
.25 
2.08 

$5.50 
3.00 
.25 
3.75 

$5.13 
2.68 
.35 
3.50 

$11.66 

Oil,  etc 

Gasolene    ...             ... 

3.00 

4.00 

Indirect  Charges 


Depreciation  

$3.50 

$4.19 

$3.60 

$3.40 

$3.67 

$4.00 

$3.77 

Interest  on  Investment  .... 

1.20 

1.26 

1.08 

1.22 

1.10 

1.00 

1.15 

Insurance  

1.50 

2.54 

1.26 

2.10 

.86 

.50 

1.47 

Garage  

1.00 

1.20 

1.00 

1.00 

.89 

1.00 

1.01 

Maintenance  

.50 

.50 

1.00 

.75 

Overhaul 

1.33 

2.75 

1.80 

1.60 

2.00 

3.00 

2.07 

License 

.17 

.27 

.20 

.20 

.20 

.20 

.20 

Body  upkeep  

.25 

.30 

.10 

.40 

.27 



10.69 

Supervision  

.50 

2.93 

2.05 

1.90 

1.90 

1.90 

Lost  Time 

2  20 

1.67 

3.40 

2.50 

1.97 

2.57 

2.57 

Total  .... 

$23.45 

$28.09 

$24  .  26 

$27.07 

$22.12 

$24.17 

$26.82 

8  GOOD  ROADS  A  BUSINESS  PROPOSITION 


THE  AMOUNT  OF  HAULAGE 

The  amount  of  haulage  that  passes  over  a  given  road  is 
quite  as  important  as  the  unit  cost,  for  it,  too,  enters  into 
the  total  cost  of  transportation.  The  "  tonnage  "  may  be 
roughly  ascertained  by  a  traffic  census,  or,  in  the  case  of  farm 
products,  by  a  computation  based  upon  the  "  traffic  area  " 
served  by  the  road  and  the  products  raised  thereon.  Either 
of  these  methods  should  be  supplemented  by  estimates  of 
persons  familiar  with  the  local  conditions,  especially  by  those 
who  make  it  a  business  to  deal  in  the  products. 

Estimating  by  Traffic  Census. — The  actual  count  of  the 
vehicles  with  their  character  and  loading  is  made  for  a  period 
or  periods  sufficiently  long,  and  varied  enough  as  to  day  of 
week  and  months  of  year,  to  secure  a  reasonably  true  average. 
The  number  of  loads,  the  average  quantity  in  tons  per  load,  the 
kind  of  vehicles  used,  and  distance  hauled  are  the  factors 
sought  to  be  ascertained.  The  enumerator  should  be  sup- 
plied with  a  ruled  tally  sheet  of  convenient  size,  along  the  left- 
hand  side  of  which  are  written,  as  far  as  it  is  possible  to  make 
out  beforehand,  the  kinds  of  vehicles  and  loads  that  are  likely 
to  pass,  with  a  few  blank  lines  left  for  others  to  be  entered.  A 
tally  mark  is  made  in  the  right  space  as  each  vehicle  passes; 
an  estimate  of  the  tonnage  based  upon  actual  weighing  of 
a  number  of  vehicles  can  be  made  up  in  the  office  later.  Table  I 
gives  a  summary  of  several  such  censuses  made  under  govern- 
mental direction. 

Estimating  by  Traffic  Area. — From  a  map  and  field  observa- 
tions the  traffic  area  served  by  a  particular  highway  is  outlined. 
The  average  crop  production  in  the  area  must  then  be  deter- 
mined and  from  these  the  traffic  tonnage  estimated.  If  the 
land  about  a  market  center  is  of  uniform  quality  and  uniformly 
farmed,  the  average  haul  might  be  estimated  from  the  mean 
distance  of  the  land  from  the  center.  For  example  consider 
the  community  market  to  be  at  the  center  of  the  circle  and  the 
territory  about  divided  into  six  sections  (Fig.  2).  The  mean 
distance  of  every  point  directly  to  the  center  is  fr=.67r;  the 


AMOUNT  OF  HAULAGE  9 

TABLE  I.— TRAFFIC  RECORD  OF  SEVEN  IMPROVED  ROADS  i 


g 

00^" 

1 

0  % 

1^ 

c 
o 

1    - 

03 

Js 

0 

Location  2 

cs 
js 

&* 

ft! 

il. 

1111 

Ji 

"2? 

3 

M 

a  ^ 

03    g 

>  c  J% 

"f^'-l 

|f 

|l 

s 

V 
H-3 

H 

•5~ 

H 

ri 

^ 

rt 

1 

Lauderdale  Co.,  Ala.  (2)  . 

28.3 

58 

10 

367,849 

228,046 

154,437 

16.0 

2 

Boone    and    Story    Co., 

Iowa  (16) 

45.1 

10 

2 

162,342 

105,662 

113,521 

37  2 

3 

Cumberland  and  Sagada- 

hoc  Co.,  Me.  (8)  

32.1 

18 

4 

227,451 

38,182 

23.6 

4 

LefloraCo.,  Miss.  (3)..  .  . 

24.1 

33 

7 

197,386 

90,628 

60,736 

36.2 

5 

Montgomery    Co.,    Md. 

(1) 

5.4 

21 

2 

14,044 

5,892 

12,531 

26  0 

6 

Muskingum  Co.,  Ohio  (2) 

20/9 

28 

6 

111,026 

132,711 

41,952' 

28.0 

7 

Jackson  Co.,  Ore.  (3)..  .  . 

50.5 

11 

4 

51,810 

32,170 

73,881 

36.6 

Totals  and  averages  .... 

206.4 

26 

5 

1,131,953 

495,235 

29.1 

1  Bulletin  136,  U.  S.  Dept.  of  Agriculture. 

2  Figures  in  parentheses  indicate  the  number  of  traffic  areas. 

radius  of  the  circle  which  will  divide  the  area  of  the  sector  into 

two   equal   areas   is    .71r;    the   mean 

distance  from  all  points  to  the  median 

line  thence  to  the  center  is  .Sir;  if  all 

parts  of  the  sector  were  squeezed  up 

and    concentrated    along  the   median 

without  changing  their  distances  from 

the  center  the  mean   would   be  .64r; 

the  center  of  gravity  of  the  sector  is 

.64r  from   the    center   of   the    circle. 

From   the   above   it  will  appear  that 

.67r    would    riot    be    far    from    the 

average  haul  when  the  distribution  of  products  is  uniform  over 

the  district. 

Tonnage. — The  number  of  tons  arising  on  these  farms  which 
is  transported  over  the  roads  varies  with  the  kind  of  crop,  the 
amount  of  stock  fed,  stock  kept  for  dairying,  and  other  local 


FIG.  2. 


10  GOOD  ROADS  A  BUSINESS  PROPOSITION 

governing  conditions.  Study  of  surveys  made  by  Cornell 
Agricultural  Experiment  Station,1  investigation  of  the  U.  S. 
Office  of  Public  Roads,2  U.  S.  Department  of  Agriculture, 
Bureau  of  Statistics,3  and  U.  S.  Census  4  lead  to  the  conclusion 
that  the  acreage  yield  of  marketable  products  is  ordinarily 
between  TV  and  \  ton  per  farmed  acre,  and  that  the  farmed  land 
is  about  60  to  65  per  cent  of  the  nominal  acreage  of  the  farm. 

A  mathematical  analysis  will  show  that  if  a  road  serves  a 
sector  of  one-sixth  of  a  circle  and  the  yield  of  marketed  products 
is  uniform  over  the  sector  the  total  tonnage  is  given  by  the 
equation 

77=335.12gr2; 

where  T=  total  tons  per  year; 

5  =  yield  of  marketed  crops  per  acre; 
r  =  maximum  haul  =  radius  of  the  circle. 

Dividing  T  by  the  number  of  working  days  per  year  gives  the 
average  daily  haul  for  that  road  into  the  market.  The  average 
length  of  haul  is  theoretically  f  r. 

The  haul  over  any  zone  may  be  taken  as  made  up  of  all  that 
tonnage  which  originates  outside  the  zone  plus  that  originating 
within  the  zone  times  its  mean  distance  from  the  inner  edge  of 
the  zone. 

These  equations  follow: 

Haul  over  any  zone  having  outer  radius  a  and  inner  radius  b 
concentric  with  the  circle  of  maximum  haul  having  a  radius  r  is 


For  the  first  mile,  a  =  l,  6  =  0, 


1  Bulletin  295,  Cornell  Agricultural  Experiment  Station. 

2  Bulletin  136,  U.  S.  Department  of  Agriculture. 

3  Bulletin  49,  Bureau  of  Statistics,  U.  S.  Dept.  of  Agri. 

4  Reports  of  the  1910  U.  S.  Census. 


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12  GOOD  ROADS  A  BUSINESS  PROPOSITION 

For  the  eighth  mile 


Table  II  is  a  tabulation  of  the  theoretical  average  tonnage  on 
each  of  six  uniformly  distributed  .market  roads  taken  from 
Bulletin  136,  U.  S.  Department  of  Agriculture. 

Mr.  E.  W.  James,  chief  of  Maintenance,  U.  S.  Office  of 
Public  Roads,  makes  an  analysis  of  the  distribution  of  traffic 
over  the  roads  of  a  township  as  laid  out  by  the  rectangular 
system  of  the  United  States  land  survey.1  The  market  place  is 
taken  to  be  at  the  center  of  the  township.  His  analysis  shows 


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S^ 

"s 

1  1  1 

—  *» 

*»»— 

21 

22 

23 

24 

Fic 

^oacfa 

}.  3. 

that  4.8  per  cent  of  the  total  mileage  carry  39.3  per  cent  of  the 
traffic;  that  9.5  per  cent  of  the  roads  carry  63  per  cent  of  the 
traffic,  and  that  14.3  per  cent  of  the  roads  carry  71  per  cent  of 
the  traffic.  He  thinks  the  analysis  corroborates  the  observa- 
tions of  engineers  to  the  effect  that  20  per  cent  of  the  roads 
carry  80  per  cent  of  the  traffic.  The  relative  importance  of  the 
type  roads  in  the  one-eighth  area  surrounding  the  center  are 
given  in  the  diagram,  Fig.  3. 

There  seems  to  be  sound  reason  for  the  high-class  improve- 
ment of  a  few  miles  of  road  near  to  the  market  center. 

Economic  Investment. — Having  determined  by  actual  traffic 

census  or  by  some  other  method  of  estimating  the  probable 

tonnage  on  any  particular  road,  the  saving  in  the  haulage  costs 

may  be  computed  provided  the  cost  of  hauling  over  the  several 

1  Engineering  Record,  Vol.  74,  p.  439.' 


MOTOR   TRANSPORT 


13 


types  of  roads  that  it  is  practicable  to  build  is  known.  The  cost 
of  hauling  on  earth  roads  is  estimated  to  be  about  20  cents  per 
ton  mile,  on  a  well-paved  road  8  to  10  cents.  Assume  the 
saving  10  cents  with  a  daily  tonnage  of  20.  The  annual  decrease 
of  haulage  cost  would  be  .10X20X300  =  1600  per  mile.  Ignor- 
ing upkeep,  the  district  could  afford  to  pay  5  per  cent  interest 
on  $12,000  to  make  this  improvement.  In  deciding  upon  the 
type  of  roadway,  maintenance  and  repair  should  be  ta,ken  into 
account,  also  the  value  of  the  improvement  to  the  non-com- 
mercial traffic.  This  is  often  of  as  much  importance  as  the 


FIG.  4. 

commercial  traffic,  and  is  more  frequently  the  final  determining 
factor  for  or  against  the  improvement. 

Especially  is  this  latter  true  since  the  character  of  rural 
road  traffic  has  changed  or  is  rapidly  changing  from  horse- 
drawn  to  motor-driven. 

Farm  Trucks  and  Motor  Transport. — The  farmers  are 
adopting,  in  addition  to  automobiles  for  passenger  travel,  light 
trucks  to  haul  produce  to  market.  (Fig.  4.)  Also  companies 
are  being  formed  to  operate  motor-transports  upon  the  hard- 
surfaced  roads  as  soon  as  they  are  constructed,  and  sometimes 
upon  earth  roads.  These  make  regular  trips  according  to  a 
published  schedule,  doing  a  business  similar  to  that  of  the 


14 


GOOD  ROADS  A  BUSINESS   PROPOSITION 


FIG.  5.— Truck  Load  of  Hogs 


FIG.  6. — Farm  Trucks  Unloading  Hogs  at  the  Market 

— Courtesy  Nebrasla  Stale  Highway  Department 


MAINTENANCE  COSTS  15 

railroads.  It  is  said  that  short-branch  railroad  lines  are  not 
paying  expenses,  and  that  the  railroads  could  well  afford  to 
give  them  up  provided  the  products  could  get  to  the  main  lines. 
The  motor  truck  seems  to  be  filling  the  need.  By  arrangement 
trucks  will  go  directly  to  the  farm  for  loading  and  unload  at 
the  main  line  railroad  station,  thus  saving  the  cost  of  one 
handling. 

With  hard-surfaced  roads  sufficiently  strong  to  hold  up 
the  larger  trucks  a  great  deal  more  freighting  will  be  done 
from  town  to  town  and  from  farm  to  market.  Figs.  5  and  6 
show  trucks  unloading  hogs  at  the  early  market  at  Omaha. 
These  hogs  have  been  hauled  some  of  them  50  miles,  but 
within  a  few  hours  after  leaving  the  farm  they  are  at  the  market 
fresh  and  in  the  pink  of  condition.  Had  they  been  taken  to  the 
local  railroad  station  they  might  have  been  twenty-four  to 
thirty-six  hours  making  the  trip,  often  without  feed  or  water. 

Maintenance  Costs. — The  cost  of  maintenance  is  as  vari- 
able as  that  of  construction.  Cost  data  are  being  better  kept 
from  year  to  year  and  probably  in  a  few  years  will  have  become 
so  standardized  that  definite  calculations  may  be  made. 
Roughly  speaking,  the  annual  cost  of  perpetually  maintaining 
in  first-class  condition  a  mile  of  road  16  feet  wide  is:1 

Earth  road $  20  to  $  40  Author's  Estimate. 

Gravel 180  to  280  Bulletin  136,  U.  S.  Agr. 

Water-bound  macadam. .  500  to  600  Bulletin  136,  U.  S.  Agr. 

Bituminous  macadam. . .  600  to  800  Bulletin  136,  U.  S.  Agr. 

Concrete  Roads  2 600  to  800  Author's  estimate. 

Brick  Pavements  3 400  to  500  Author's  estimate. 

Asphalt  Pavements  3 600  to  800  Author's  estimate. 

Upon  such  figures  it  would  not  usually  be  a  strictly  econom- 
ical proposition  to  build  hard  roads  unless  the  traffic  is  of  con- 
siderable amount.  For  example,  if  the  upkeep  of  an  earth 
road  is  $50  per  mile  and  that  of  a  bituminous  macadam  $450, 
the  saving  in  haulage  would  have  to  be  $400,  or  there  will  have 

1  Based  on  pre-war  prices.     Should  be  practically  doubled  now,  1920. 

2  The  life  of  a  concrete  road  has  not  yet  been  determined. 

3  Based  on  a  life  of  twenty-five  years. 


•16  GOOD  ROADS  A  BUSINESS  PROPOSITION 

400 
to  be  an  annual  tonnage  of  about  —  =4000,  or  an  average  daily 

tonnage  of  133.  This  amount  is  frequently  exceeded  by  roads 
leading  into  important  market  centers. 

As  intimated  above,  the  convincing  need  for  good  roads 
is  more  social  than  economic.  The  better  road  pays  for  the 
same  reason  that  it  pays  to  live  in  a  good  house,  that  it  pays  to 
wear  good  clothes;  it  pays  in  advertising  one's  community;  it 
pays  in  self-respect,  self-satisfaction,  comfort,  and  pleasure; 
just  as  all  upward  trends  in  civilization  pay.  The  advent  of 
the  automobile  most  clearly  demonstrated  this.  In  the  great 
agricultural  communities  of  the  Middle  West,  nearly  every 
farmer  owns  a  motor  car.  And  while  this  has  proven  itself 
advantageous  in  that  he  can  run  into  town  and  back  for  mail, 
supplies,  or  minor  repairs,  or  do  the  daily  marketing  of  his 
cream,  eggs,  and  perishable  products,'  while  the  horses  he  uses 
for  farming  are  feeding  and  he  is  resting,  nevertheless  the 
machine  was  purchased  primarily  for  social  enjoyment.  It  is 
not  at  all  unusual  for  farmers  and  their  families  to  drive  20 
miles  into  town  after  supper  to  enjoy  a  concert,  to  attend  a 
lecture  or  theater  or  church  service,  or  merely  to  visit  with 
neighbors  and  friends.  They  return  home  in  tune  for  sleep, 
better-natured  and  happier  because  of  the  recreation  and  the 
invigorating  influence  of  rapid  motion  through  pure  air.  The 
motor  car  has  virtually  lessened  distance.  The  farmer  who  now 
lives  ISThiles  from  his  community  center  is  practically  no  more 
remote  than  was  formerly  the  one  living  3  miles.  Of  course, 
this  argument  presupposes  good  roads.  The  instant  the  roads 
become  so  poor  the  machine  cannot  be  used,  the  original  state 
of  isolation  obtains.  It  is  no  wonder,  then,  that  every  owner 
of  a  motor  car  becomes  a  good  roads  advocate. 

To  sum  up:  Good  roads  constitute  a  profitable  business 
proposition. 

For  the  Farmer: 

1.  More  remunerative  perishable  and  high-acre  value 
crops  can  be  raised,  thus  allowing,  also,  diversi- 
fication of  crops. 


SUMMARY  17 

2.  Cost  of  hauling  will  be  decreased. 

3.  Can  sell  on  the  high  market. 

4.  Children  can  attend  school. 

5.  Family  can  attend  church. 

6.  Physician  will  be  constantly  at  hand. 

7.  Will  have  better  mail  service. 

8.  More  social  life. 

9.  Boys  and  girls  contented  to  remain  on  farm. 
10.  Material  increase  in  value  of  land. 

Railroad  Man: 

1.  Improved  roads  mean  greater  aggregate  production, 

consequently  more  railway  traffic. 

2.  Prevent  freight  congestion. 

3.  Promote  new  industries. 

4.  Attract  tourists. 

Publisher  and  Editor : 

1.  Improved  roads  by  making  possible  rural  delivery 

increase  the  circulation  of  newspapers  and  maga- 
zines. 

2.  Advertising  columns  are  in  greater  demand. 

3.  If   advertising   pays   all   commercial   interests   are 

stimulated. 

Hotel  Proprietor: 

Better  roads  mean  more  tourists  and  business  travelers. 

Touring  by  railway  and  automobile  is  rapidly  becoming 
a  national  pastime.  Soon  it  will  be  all  but  uni- 
versal. 

The  Commercial  Traveler: 

With  automobile  and  good  roads  he  can  double  the 
number  of  towns  he  makes  per  day. 

The  User  of  an  Automobile  and  Motor  Truck: 

1.  Gets  the  benefit  of  the  machine  every  day. 

2.  Time  on  road  is  minimized. 

3.  Longer  tours  projected  with  assurance. 
4.-  Maintenance  costs  are  decreased. 


18  GOOD  ROADS  A  BUSINESS  PROPOSITION 

5.  Larger  loads  may  be  carried. 

6.  Deliveries  made  more  quickly  and  more  regularly. 

7.  General  cost  of  transportation  per  passenger  decreased. 

8.  Pleasure  and  health  enhanced. 

Manufacturer  and  dealer  in  wagons,  buggies,  and  automobiles: 
Every  mile  of  improved  road  means  a  greater  demand 
for  these  vehicles. 

Manufacturer  and  dealer  in  road  machinery  and  road-making 
materials : 

The  roads  cannot  be  improved  without  their  products. 

Manufacturer  and  dealer  in  all  sorts  of  building  materials  and 

supplies,  hardware  and  furniture: 

Increased  prosperity  of  farmers,  merchants,  and  men  of 
ether  callings  and  pursuits  means  a  demand  for 
newer,  larger,  and  better  houses,  barns,  sheds,  and 
garages;  for  modern  and  efficient  conveniences, 
applications,  and  furnishings. 

Manufacturer  and  dealer  in  dry  goods,  groceries,  jewelry, 
drugs,  musical  instruments — in  short,  all  forms  of  mercantile 
and  manufacturing  business : 

Because  good  roads  are  commercial  feeders  and  every 
improvement  in  these  roads  means  greater  pros- 
perity, raises  the  standard  of  living,  and  produces 
new  wants  which  must  be  supplied. 

There  is  no  one  thing,  unless  it  be  the  public  school,  that  is  of 
such  universal  interest  and  importance  to  the  whole  people 
as  the  common  road.  The  money  spent  in  the  proper  improve- 
ment of  it  is  an  investment  which  will  return  large  annual 
interest  in  reduced  costs  of  transportation,  greater  freedom  of 
traffic  and  travel,  closer  social  intercourse  between  neighbor 
and  neighbor,  between  town  and  country,  and  increased  joy, 
comfort,  and  happiness. 


CHAPTER  II 
ROAD  LOCATION 

THE  laying  out  of  a  road,  whether  it  be  intended  for  wagon 
and  horses,  automobile  or  locomotive,  is  largely  an  engineering 
problem.  In  many  of  the  Western  States  the  roads  have  been 
"  located  by  law  "  upon  section  lines.  In  doing  so,  no  thought 
whatever  was  given  to  the  road  as  a  usable  thing,  as  an  agency 
for  efficiency  in  marketing  the  products  of  the  farm,  as  a  means 
for  rapid  communication  with  neighbor,  dealer,  or  consumer,  as 
an  instrumentality  for  hastily  securing  the  services  of  the 
physician  or  spiritual  adviser,  as  an  aid  to  the  education  of  the 
growing  and  incipient  citizen,  or  as  a  means  of  pleasure  and 
comfort  to  those  who  must  perforce  travel  thereon.  The 
section-line  scheme  of  road  location  thought  primarily  of  the 
convenient  rectangular  division  of  land  and  secondly  of  placing 
a  road  near  every  farm.  The  final  result  is  that  there  is  being 
wasted  in  unused  and  unnecessary  roadways  at  least  one-half 
of  all  the  land  set  aside  for  road  purposes. 

Ill  the  Eastern  and  Southern  States,  on  the  other  hand, 
many  old  trails  have  expanded  into  crooked  and  inconvenient 
roadways.  The  day  is  near  when  it  will  be  deemed  wise  to 
relocate  the  principal  highways  leading  to  market  and  trading 
centers.  Why  not  learn  a  lesson  from  nature?  A  stream 
flows  along  the  path  of  least  resistance,  winding  from  side  to 
side  so  that  it  will  not  unduly  tear  up  its  bed  and  destroy  its 
banks,  thus  performing  its  business  of  transporting  water  with 
an  economy  worthy  of  imitation  by  the  most  skilled  managers. 
The  stream  goes  the  most  direct  way  possible,  passing  around 
hills  and  cutting  away  the  soil  until  the  grade  is  commensurate 

19 


20  "ROAD   LOCATION 

with  the  velocity.     That  is  what  should  be  done  with  the  high- 
ways, streams  of  travel  and  commerce. 

There  are  some  general  principles  that  will  apply  to  the 
location  or  relocation  of  a  road,  but  it  must  always  be  borne  in 
mind  that  local  conditions  are  largely  the  determining  factors, 
that  economic  questions,  frequently,  must  give  way  to  other 
considerations  such  as  pleasure  and  ease,  or  the  vested  rights 
of  land  owners.  It  might  be  well,  also,  if  the  locator  "  dipt  into 
the  future,  far  as  human  eye  could  see,"  and  built  for  the  many 
generations  this  road  is  expected  to  serve,  ever  remembering 
that  future  changes  will  continually  increase  in  difficulty  and 
expense. 

GENERAL  PRINCIPLES  OF  LOCATION 

Directness. — Undoubtedly  the  shortest  line  compatible 
with  easy  grades  and  proper  drainage  should  be  selected,  for 
thus  the  interest  on  first  cost  and  the  annual  charge  for  main- 
tenance and  operation  will  be  least.  While  the  value  of  direct- 
ness is  of  prime  importance,  it  may  be  overestimated.  Often 
it  is  not  much  farther  around  a  hill  than  over  it.  The  bail  of  a 
bucket  is  no  longer  when  lying  horizontally  than  when  standing 
vertically.  A  road  may  even  vary  considerably  from  a  straight 
line  and  not  materially  increase  its  length.  The  statement  of 
Gillespie,  published  as  long  ago  as  1847,  is  often  quoted:  "  If  a 
road  between  two  places  10  miles  apart  were  made  to  curve  so 
that  the  eye  could  nowhere  see  more  than  a  quarter  of  a 
mile  of  it  at  once,  its  length  would  exceed  that  of  a  perfectly 
straight  road  between  the  same  points  by  only  about  150 
yards." 

The  saving  due  to  a  difference  in  length  can  be  computed 
only  when  the  cost  of  hauling  and  the  amount  of 
traffic  on  that  particular  road  are  known.     For  ex- 
ample, suppose  it  is  desired  to  find  out  whether  it 
,.,     7        will  pay  to  relocate  a  road  now  going  along  two  sides 
of  a  quarter-section  of  land,  diagonally  through  the 
section,  the  traffic  being  3000  tons  per  year  and  the  cost  of 
hauling  20  cents  per  ton  mile.     (Fig.  7.) 


•&  ml. 


DIRECTNESS  AND  GRADES  21 

Annual  cost  of  hauling  along  the  two  sides: 

One  mile  (3000X.20X1) . . $600 

Diagonal  distance  (|xV2)  =  .71  mile. 

Annual  cost  hauling  through  (3000  X  .20  X  .71)  ...     426 


Difference  in  cost $174 

Assuming  these  roads  to  be  4  rods  wide,  they  occupy  8 
acres  per  mile. 

Acres 

Around  the  field  (8X1) 8.00 

Through  the  field  (8X.71) 5.68 


Difference r  2.32 

If  this  land  rents  at  $5  per  acre,  there  will  be  a  saving 
of  2.32X$5  =  $11.60,  which  makes  a  total  annual 
saving  of $185.60 

This  is  5  per  cent  interest  on.  . $3,712.00 

This  amount  could  be  expended  by  the  community  for  the 
purpose  of  this  improvement  and  still  be  no  worse  off  financially 
than  before.  It  should  be  remembered  that  all  computations 
of  this  sort  must  be  taken  as  approximations,  but  can  be  used 
in  connection  with  local  considerations  to  aid  in  reaching  a 
decision. 

Grades.  Definition. — The  grade  of  a  road  is  the  rate  of 
rise  or  fall  and  is  usually  expressed  in  rise  or  fall  per  hundred 
or  per  cent.  Everyone  knows  that  it  is  easier  to  pull  a  load  on 
the  level  than  up  a  hill,  therefore,  other  things  being  equal,  grades 
should  be  reduced  as  much  as  possible.  However,  the  first 
cost  of  a  longer  and  flatter  grade  may  offset  any  advantage,  or 
drainage  may  be  the  determining  factor.  Each  particular 
case  must  be  studied  by  itself.  There  are  some  mechanical 
formulas  that  can  be  applied,  but  too  much  reliance  must  not 
be  placed  on  them,  for,  while  the  mathematics  is  absolutely 
correct,  the  assumptions  necessary  for  their  application  may  be 
erroneous. 


22  ROAD  LOCATION 

The  load  which  a  horse  can  pull  up  a  hill  is  given  by  the 
formula 


To  demonstrate  this, 

Let  jP  =  tractive  force  of  horse  along  the  road; 
W  =  weight  of  horse; 

L=load  pulled,  including  weight  of  vehicle; 
n  =  coefficient  of  road  resistance; 
a  =  angle  of  incline; 
g  =  grade  of  incline  =  tan  a; 

T 
t  =  Tp  =  tractive  force  in  terms  of  weight  of  horse. 

The  work  of  moving  a  load  from  0  to  B 
M    equals  the  work  of  moving  it  from  0  to  A  plus 


FIG.  8.  the  work  of  lifting  it  from  A  to  B.     (Fig.  8.) 

Work  from  0  to  B  =  T(OB)  ; 
Work  from  0  to  A  =  nL(OA)  ; 
Work  from  A  to  B=(W  +  L)AB; 


=  juL  cos  a-f  (TF+  L)  sin  a. 
Whence 

--  tan  a 
L  =  coso  - 

ju+tan  a 

or,  since  for  small  angles  cos  a  does  not  differ  materially  from 
unity 

.........     (1) 


It  is  generally  asserted  that  a  horse  working  day  after  day 
can,  without  injury  to  himself,  exert  a  direct  pull  on  the  traces 
of  about  one-tenth  his  own  weight,  and  that  for  a  short  space 


EFFECT  OF  GRADE  ON   LOAD 


23 


of  time  he  is  capable  of  doubling  this  amount.  It  has  also 
been  determined  by  experiment  that  the  direct  pull  necessary 
to  draw  a  load  at  slow  speed  on  the  level  in  well-lubricated 
wagons  i»  approximately  as  follows: 


Lbs.PerTon 

M  =  Coef.  of 
Resist. 

Upon  Steel  rails  

10 

Sheet  asphalt  

20 

Asphaltic  macadam  

20 

Concrete  •  

20 

Brick.  . 

20 

_L_ 

Broken  stone  water-bound  macadam.  .  . 
Earth,  best  condition  

30 
67 

alTo 
T5 

Earth,  medium  condition 

100 

i 

Earth,  poor  condition  

300 

A 

Grade  Per  Cent 


FIG.  9.— Showing  the  Load  in  Terms  of  W  (the  Weight  of  the  Horse)  that 
May  be  pulled  Up-grade  by  Exerting  a  Force  of  1/10  W 


24 


ROAD  LOCATION 


Using  these  values  and  Equation  (1),  Tables  I  and  II  have 
been  computed.  Figs.  9  and  10  are  graphs  drawn  from  these 
tables.  To  one  used  to  reading  graphs  it  is  immediately  evident 
that  the  effect  of  grade  is  very  much  greater  for  a  smooth 
than  for  a  poor  road,  that  is,  the  effect  is  much  more  for  those 
roads  having  a  small  coefficient  of  resistance.  The  harder. and 
smoother  the  roads,  the  greater  need  of  reducing  the  grades. 


345 
Grade  Per  Cent 


10 


Fia.  10. — Showing  the  Load  that  a  Horse  Can  Pull  by  Exerting  a  Force 
of  1/10  His  Own  Weight  up  a  Grade  in  Terms  of  the  Load  He  can 
Pull  on  a  Level  Road  of  the  Same  Condition 

It  will  be  noticed  that  the  advantage  on  traction  of  a  smooth 
road  is  not  particularly  manifest  for  grades  greater  than  4 
per  cent,  but  is  very  marked  as  the  grades  become  smaller  and 
smaller.  It  might  be  well  to  notice,  however,  that  always  for 
every  grade  a  larger  load  may  be  pulled  upon  the  smooth  hard 
road  than  on  the  poor  road.  Again,  the  reader  must  be  cau- 
tioned that  all  calculations  such  as  this  should  be  considered 
with  judgment  in  the  light  of  the  particular  case  in  hand. 


TRACTIVE   RESISTANCE   DUE   TO   GRADES 


25 


TABLE  I 

Showing  the  load  in  terms  of  W  (weight  of  horse)  that  may  be  pulled  up- 
grade by  exerting  a  force  of  1/10  W. 


Grade 

-T) 

TRACTIVE  RESISTANCE  IN  POUNDS  PER  TON 

Per 
Cent 

10 

20 

30 

40 

60 

100 

300 

0 

20.00 

10.00 

6.67 

5.00 

3.33 

2.00 

-.67 

1 

6.00 

4.50 

3.60 

3.00 

2.25 

1.50 

.56 

2 

3.20 

2.67 

2.29 

2.00 

1.60 

1.14 

.47 

3 

2.00 

1.75 

1.56 

1.40 

1.17 

.87 

.39 

4 

1.33 

.    1.20 

1.09 

1.00 

.86 

.67 

.32 

5 

.91 

.83 

.79 

.71 

.62  ' 

.50 

.25 

6 

.62 

.57 

.56 

.50 

.44 

.36 

.19 

7 

.40 

.38 

.35 

.33 

.30 

.25 

.14 

8 

.24 

.22 

.21 

.20 

.18 

.16 

.09 

9 

.15 

.10 

.10 

.09 

.08 

.07 

.04 

10 

.00 

.00 

.00 

.00 

.00 

.00 

.00 

TABLE  II 

Showing  the  load  that  a  horse  can  pull  by  exerting  a  force  of  1/10  his  own 
weight  up  a  grade  in  terms  of  the  load  he  can  pull  on  a  level  road  of 
the  same  condition. 


TRACTIVE  RESISTANCE  IN  POUNDS  PER  TON 


Grade 
Per 
Cent 

10 

20 

30 

40 

60 

100 

300 

0 

1.00 

1.00 

1.00 

1.00 

1.00 

1.00 

1.00 

1 

.30 

.45 

.54 

.60 

.68 

.75 

.84 

2 

.16 

.27 

.34 

.40 

.48 

.57 

.71 

3 

.10 

.18 

.23 

.28 

.35 

.44 

.58 

4 

.07 

.12 

.16 

.20 

.26 

.33 

.47 

5 

.04 

.08 

.12 

.14 

.19 

.25 

.37 

6 

.03 

.06 

.08 

.10 

.13 

.18 

.28 

7 

.02 

.04 

.05 

.07 

.09 

.12 

.21 

8 

.01 

.02 

.03 

.04 

.05' 

.08  • 

.13 

9 

.01 

.01 

.01 

.02 

.03 

.04 

.06 

10 

.00 

.00 

.00 

.00 

.00 

.00 

.00 

26 


ROAD   LOCATION 


Slipperiness  or  poor  foot-hold  might  materially  change  these 
values,  and  this  may  depend  upon  the  weather. 

In  Equation  (1)  no  account  was  taken  of  increased  work  of 
moving  the  horse,  that  is  the  motive  power,  itself  due  to  the 
condition  of  the  road  surface.  Were  a  formula  to  be  derived 


77>t<5ffffe  /Off£7ftyi//re3  fo/x/// /fcxere 

firs?  c/ass  earrfr    .  M 

road 


FIG.  11. — A  Load  that  One  Horse  can  Pull  on  the  Level  Requires  Eight 
Horses  on  a  10  Per  Cent  Grade 

for  tractors  or  automobiles,  this  would  enter  and  the  formula 

be  changed. 

Using  the  same  notation  as  on  page  22 
with  the  exception  that  W  now  =  the  weight 
of,  and  F  =  the  force  exerted  by  the  tractor  or 
automobile,  there  results: 

Work  of  drawing  load  L  with  tractor  weighing 

W  from  0  to  B =F(OB) 


Work  of  moving  along  OA =  n(W+L)OA 

Work  of  lifting  along  AB =(W+L)AB 


=  (fjL  cos  a+sin  a)  (TF+L) 

=  (M+00  (W+L)  approximately; 

F 
=  -^-W. 


(2) 


. 
LOAD  A  TRACTOR  CAN  PULL  UPGRADE      27 

EXERCISES 

What  load  can  a  gasoline  tractor  weighing  12  tons,  exerting  20  H.P., 
traveling  over  a  good  earth  road  at  a  speed  of  3  miles  per  hour,  haul  up  an 
incline  of  3  ft.  in  a  hundred? 

A  H.P.  is  defined  as  doing  work  at  the  rate  of  33,000  ft.-lb.  per  minute, 
or  33,000  X 60  ft.-lb.  per  hour. 

20  H.P.,  therefore,  is  33,000X60X20  ft.-lb.  per  hour. 

If  the  force  exerted  by  the  tractor  is  F,  the  work  performed  per  hour  is 
3  X 5280  XF  ft.-lb. 

.'.     3  X5280XF  =  33,000X60X20 

c,_33,OOOX60X20_20,000_0_nn 
"3X5280-       ~8~ 

Substituting  in  Equation  (2), 

OKAA 

L  =  T0^3 — 24,000  =  31,250-24,000 

2000 +Io6 
=  72501b. 

2.  If  the  engine  could  continue  to  exert  the  same  force,  at  what  speed 
would  it  haul  this  same  load  over  a  level  road?  Ans.  11  miles  per  hour. 

[NOTE  :  -  The  above  examples  tacitly  assume  the  coefficient 
of  resistance  remains  constant.  As  a  matter  of  fact,  deter- 
mined by  experiment,  the  force  necessary  to  project  a  body 
through  a  resisting  medium  varies  approximately  as  the  square 
of  the  velocity,  so  that  11  miles  Would  be  too  large.] 

It  has  been  assumed  above  that  a  horse  can  exert  for  the 
period  of  a  working  day  one-tenth  his  weight.  For  short 
periods  of  time  this  may  be  materially  increased ;  for  moderate 
periods  it  might  be  doubled,  for  very  short  periods  quadrupled. 
Solving  Equation  (1)  for  g  gives  the  grade  up  which  any  par- 
ticular load  can  be  hauled.  Thus 

_tW-»L 

g~  W+L'  . 

If  the  tractive  force  be  increased  n  times, 

•••••••     (3) 


28  ROAD  LOCATION 


EXERCISES 

1.  On  a  level  steel  track  (Table  I)  a  load  of  20  W  can  be  hauled;  up 
what  grade  can  the  same  load  be  hauled  if  the  tractive  force  be  doubled? 

Substituting  in  (3)  g=-rns  or  about  £  of  1  per  cent,  which  might  be 
considered  the  limiting  grade  of  a  steel  track  if  the  load  on  the  level  is 
to  be  a  maximum. 

2.  Under  similar  conditions  what  would  be  the  limiting  grade  for  an 
earth  road  in  good  condition?  Ans.  g  =  3%  per  cent. 

3.  What  would  be  the  limiting  grades  if  the  tractive  force  be  quad- 
rupled? Ans.  Steel  track,  1.4  per  cent;  earth,  10  per  cent. 

This  last  example  shows  why,  if  the  hill  is  short  and  the  rest  of  the  road 
is  comparatively  level,  it  would  pay  to  use  a  snatch  team  for  the  hill. 

Rise  and  Fall. — By  rise  and  fall  is  meant  the  vertical  height 
through  which  the  load  must  be  lifted  in  traversing  the  road  in 
either  direction.  If  a  road,  otherwise  level,  passed  over  a  hill 
20  feet  high,  the  rise  and  fall  is  defined  as  20  feet.  The  mini- 
mum amount  of  rise  and  fall  upon  any  particular  stretch  of  road 
is  the  difference  in  elevation  of  its  terminals.  Any  additional 
rise  and  fall  may  be  considered  avoidable  and  in  the  location  of 
the  road  whether  it  will  pay  to  avoid  it  will  depend  again  upon 
local  conditions.  If  the  work  necessary  to  raise  the  load  ver- 
tically through  the  avoidable  rise  and  fall  be  computed  and 
that  compared  with  the  work  necessary  to  move  the  load  on  the 
unavoidable  gradient,  the  rise  and  fall  may  be  expressed  in 
terms  of  distance.  For  example,  to  raise  1  ton  1  foot  high 
requires  the  expenditure  of  2000  foot-pounds  of  work,  and  taking 
the  tractive  resistance  on  an  ordinary  earth  road  as  100  pounds 
per  ton,  there  will  be  100  foot-pounds  of  work  expended  in 
drawing  a  ton  load  1  foot;  therefore,  to  balance  the  work  done 
in  overcoming  1  foot  of  rise  and  fall  the  load  must  be  drawn  on 
the  level  a  distance  of  2000 -MOO  =  20  feet.  The  better  the 
road  surface,  the  more  it  may  be  lengthened. 

EXERCISES 

1.  Using  the  coefficients  of  resistance  given  on  page  23,  determine  the 
distances  level  roads  might  be  lengthened  to  avoid  1  foot  of  rise  and  fall. 
Ans.  Steel  rails,  200  feet;    asphalt,    asphaltic  macadam,  concrete,  brick, 

100  feet;   broken  stone  macadam,  67  feet;   earth,  best  condition,  30  feet; 

earth,  medium  condition,  20  feet;  earth,  poor  condition,  7  feet. 


THE  ECONOMY  OF  ELIMINATING   GRADES 


29 


2.  Two  farms  are  each  5  miles  from  the  market,  as  indicated  on  the 
map,  but  the  road  to  one  has  a  rise  and  fall  of  132  feet,  the  other  of  396  feet. 
What  is  the  virtual  distances  of  these  farms  from  town? 

Ans.  (M  =  100  Ib.  per  ton)  5|  and  6|  miles. 

Take  the  case  heretofore  referred  to,  page  20,  of  a  diagonal 
road  through  a  quarter  section.  If  in  going  around  as  shown 
in  the  pen  sketch,  Fig.  12,  the  road  goes  up  and  down  a  hill  of 
50  feet,  say,  the  work  of  going  up  that  hill  would  be  equivalent 
to  traveling  50X20=1000  feet;  and  if  the  hill  is  so  steep  a 
brake  must  be  applied,  or  the  horses  must  hold  the  vehicle 
back,  the  descent  furnishes  practically  the  same  work  as  the 


FIG.  12. — Frequently  a  Road  May  be  Shortened  and  Two  Hills  and  a 
Sharp  Angle  Eliminated  by  Cutting  across  a  Corner 

ascent  and  there  must  be  added  another  1000  feet,  so,  by  elim- 
inating, with  the  diagonal  road,  both  hills,  there  is  a  saving  of  .38 
mile.  Add  this  to  the  .29  saved  by  cutting  diagonally  across 
and  it  gives  a  total  saving  of  .67  or  two-thirds  of  a  mile  on  this 
one  quarter-section  of  land.  Put  on  a  cash  basis  this  means 
using  the  same  assumption  as  before,  a  saving  of  14  cents  for 
each  ton  of  traffic  or  $420  for  3000  tons  annually.  A  total 
saving  including  the  rental  value  of  the  land  of  $431.60.  There- 
fore, there  could  be  borrowed  to  make  the  improvement,  at 
5  per  cent  interest,  the  sum  of  $8600.  Many  a  road  following 
the  section  line  crosses  a  series  of  foothills  which  could  be 
avoided  by  moving  it  a  short  distance  one  way  or  the  other 
to  the  comparative  level  land  of  the  valley  or  the  ridge,  thus 


30 


ROAD   LOCATION 


materially  saving  distance,  time  and  money.  Fig.  13  is  a  pen 
sketch,  by  the  author,  of  a  road  that  might  have  been  made 
nearly  level  by  moving  it  parallel  to  itself  a  quarter-mile  either 
way. 

Many  roads  in  our  plains  country  have  steeper  grades 
than  do  the  mountainous  roads  of  Switzerland.  The  roads  of 
France  are  classified: 

National  roads  (most  important),  not  exceeding 3 per  cent. 
Department  roads,  not  exceeding  4  per  cent. 
Subordinate  roads,  not  exceeding  5  per  cent. 


FIG.  13. — Some  Roads  Run  Up  and  Down  Hill  When  by  Moving  Them 
One  Way  or  the  Other  They  Might  be  Put  on  a  Comparatively  Level 
Orade. 

Minimum  Grade.— A  perfectly  level  road,  other  things  being 
equal,  would  be  best  to  travel  over,  but  for  the  purposes  of 
drainage  a  small  longitudinal  grade  is  not  only  allowable  but 
desirable.  All  road  men  know  that  a  road  going  up  a  small 
hill  is  much  easier  to  maintain  than  the  level  one  across  the 
bottom.  Engineers  pretty  generally  agree  "that  the  grade 
should  never  be  less  than  three-fourths  of  1  per  cent. 

In  order  to  save  expense,  it  is  taken  for  granted  that  the 
center  line  of  the  road  is  made  to  conform  as  nearly  as  possible 
with  the  natural  surface  of  the  ground.  To  determine  whether 
or  not  it  is  better  to  go  around  a  hill  or  cut  through,  the  interest 
on  the  difference  in  the  cost  of  construction  and  right -of  way  of 


SURVEYING  THE  ROAD  31 

the  two  lines  must  be  compared  with  the  difference  in  operating 
and  maintenance  expenses. 

There  are  many  roads  leading  out  from  the  larger  towns 
which  it  would  pay  to  relocate,  and  very  frequently  more  direct 
lines  and  easier  grades  could  be  obtained  by  locating  roads  in 
the  general  direction  of  water  courses  either  in  the  valleys  or 
upon  the  ridges  between,  thus  avoiding  unnecessary  ascents 
and  descents  which  waste  power  and  energy.  It  is  there,  too, 
most  easy  to  make  the  line  conform  to  the  original  ground  sur- 
face and  save  the  expense  of  cuts  and  fills. 

Obstacles. — New  locations  should  strive  to  cross  all  obstacles 
right  at  angles;  skew  structures  are  expensive.  On  the  other 
hand  bridges  and  culverts  not  in  line  with  the  general  trend  of 
the  road  are  dangerous.  Likewise  grade  crossings  of  railroad 
and  trolley  lines  should  be  avoided  wherever  possible. 

LAYING  OUT  THE  ROAD 

Reconnoissance. — Under  this  head  may  be  placed  the  pre- 
liminary investigations  necessary  to  familiarize  the  locator 
with  the  country  and  local  conditions  under  which  the  work 
must  proceed.  A  note  book  in  which  to  keep  full  records  is 
necessary.  Some  of  the  points  to  be  considered  are  amount  and 
character  of  the  traffic  in  each  direction;  the  general  topographical 
and  geological  features  of  the  country  through  which  the  road 
is  to  be  run,  foundation,  and  drainage;  a  knowledge  of  the 
desires  and  rights  of  the  people  living  along  the  proposed  line 
as  to  location  and  the  material  of  which  they  desire  the  road  to 
be  constructed;  materials  at  hand  and  those  that  must  be 
shipped  in,  with  freight  rates  and  unloading  facilities;  and  such 
other  matters  as  the  local  conditions  indicate. 

Preliminary  Survey. — Having  in  mind  the  general  features 
of  the  country,  including  location  and  approximate  elevation  of 
all  low  passes;  the  trend  of  streams  and  ridges,  conditions  as 
to  drainage,  soil  characteristics,  bridge  sites,  railway  crossings, 
and  pther  determining  features,  a  preliminary  survey  is  run. 
Sometimes  several  such  lines  must  be  run  before  a  definite 


32  ROAD  LOCATION 

location  is  decided  upon.  The  better  the  advance  knowledge 
the  fewer  preliminary  surveys  will  be  necessary.  In  the  relo- 
cation of  most  roads  slight  changes  only  are  necessary  and 
these  may  be  accomplished  by  a  single  survey.  In  locating 
new  roads,  however,  methods  developed  in  locating  railroads 
can  be  resorted  to  advantageously. 

The  reconnoissance  was  for  the  purpose  of  gaining  general 
knowledge  of  a  considerable  area  through  which  a  road  is  to  be 
run.  The  preliminary  survey  is  to  furnish  more  accurate 
information  of  a  narrow  zone  through  which  the  road  is  to  run. 
The  preliminary  transit  line  or  traverse  is  the  base  line  on 
which  to  tie  the  information  obtained.  Since  the  completed 
road  is  to  occupy  this  zone  the  random  transit  line  is  a  first 


FIG.  14. 

guess  at  the  best  location  of  the  line,  it  being  understood  that 
final  location  is  the  last  word  regarding  the  best  location  under 
controlling  local  conditions.  The  last  word  will  vary  con- 
siderably from  the  first  guess,  but  the  nearer  the  first  guess,  the 
better  the  "  land  judgment "  of  the  engineer,  the  less  the 
expense  for  surveys. 

Stationing. — The  preliminary  line  generally  consists  of  a 
series  of  straight  lines,  technically  called  tangents,  A  BCD. 
(Fig.  14.)  Where  the  change  in  direction  is  considerable  some 
locators  run  in  curves  to  make  the  stationing  better,  but  for 
preliminary  surveys  it  is  just  as  well  to  use  several  short  tan- 
gents. Stakes  are  driven  on  the  line  every  100  feet  apart, 
thus  determining  "  stations."  The  stakes  are  numbered 
beginning  at  0  and  continuing  1,  2,  3,  etc.;  so  that  the  number 
of  the  station  indicates  the  distance  from  the  beginning,  station 


STATIONING,   STATES,   GRADES 


33 


4  being  400  feet;  station  9,  900  feet,  etc.  A  point  between 
two  stations  is  designated  by  the  number  of  the  last  station  plus 
the  distance  from  that  station  to  the  point,  thus  3+63  indicates 
a  point  63  feet  beyond  station  3.  At  the  point  B  the  line 
changes  direction,  the  deflection  angle  E' EC  being  to  the  right 
and  is  recorded  R  29°  32'.  The  point  B  being  at  4+40,  the 
next  station  5  would  be  60  feet  from  B  on  the  line  BC.  The 
stationing  is  then  continued  in  regular  order  to  C,  thence  on 
the  line  CD,  etc. 

Stakes. — The  stakes  driven  along  the  line  of  a  preliminary 
survey  need  not  be  very  substantial,  carpenter's  laths  cut  in 
three  do  very  well.  Hubs  are  short  stakes  driven  nearly  flush 


Right  Method 


Wrong  Method 


FIG.  15. 

with  the  ground  at  points  where  the  instrument  is  set  up,  and 
should  present  a  top  about  1J  inches  square.  A  stake  called  the 
marker  is  always  driven  near  the  hub.  The  stakes  are  clearly 
marked  near  the  top  with  the  letter  indicating  the  line  and  the 
station  number.  If  a  hub-marker,  a  A,  indicating  instrument 
point,  is  placed  before  the  letter.  The  numbers  should  read 
from  the  top  toward  the  bottom  and  be  so  near  the  top  that 
there  is  no  danger  of  their  being  covered  up  in  the  ground. 

Grades  or  gradient  is  a  term  used  to  indicate  the  slope  of 
the  roadway  and  is  usually  expressed  in  per  cent  or  the  number 
of  feet  rise  or  fall  per  hundred  feet  horizontal.  A  rise  of  24  feet 
in  600  feet  =  ^jL  =  T§-o=4  per  cent  grade.  A  fall  is  given  the 
negative  sign.  Bringing  a  roadway  to  grade  is  called  grading, 


34  ROAD  LOCATION 

and  is  a  part  of  the  work  of  constructing.  The  ruling  or  limiting 
grade  is  the  steepest  grade  allowed  on  the  particular  road  in 
hand.  Maximum  grade  is  the  steepest  grade  used  in  the  survey 
and  may  or  may  not  be  the  limiting  grade.  Since  it  takes  force 
to  turn  a  vehicle,  the  grades  on  curves  should  always  be  less  than 
the  ruling  grade;  making  them  less  is  called  compensating. 

Party  Organization. — The  number  of  men  in  and  the  organi- 
zation of  the  party  will  depend  upon  the  character  and  magni- 
tude of  the  work  and  may  vary  from  thirty  in  large  parties  to 
two  in  small.  In  large  parties  separate  sub-parties  have 
charge  of  the  several  parts  of  the  work — transit,  level  and  topog- 
raphy, with  draughtsmen,  cooks,  teamsters,  and  other  camp 
followers.  The  transit  party  under  its  head  officer  will  run  in 
the  preliminary  line.  He  receives  general  directions  as  to 
location,  controlling  points,  etc.,  from  the  chief  over  him,  if 
there  be  one.  Such  directions  should  be  explicitly  noted  on 
sketches  or  the  best  map  of  the  region  available.  The  transit 
man  will,  however,  have  plenty  of  opportunity  to  use  his  judg- 
ment in  running  the  line. 

Works  on  surveying  give  directions  for  the  use  of  the  instru- 
ment, but  for  handy  reference  here  are  given  briefly  the 

OPERATIONS  OF  TAKING  PRELIMINARY  TRAVERSE 

Transit  Man. — The  ordinary  party  will  be  in  charge  of  the 
transit  man,  who  will  have  sufficient  assistants  for  the  magni- 
tude of  the  job. 

Operation. — Set  up  the  transit  at  A,  Fig.  16;  clamp  the 
vernier  at  0;  loosen  the  lower  motion;  sight  upon  B;  tie  in  the 
point  A  (that  is,  relate  it  to  a  previous  survey,  U.  S.  govern- 
ment land  system,  the  layout  of  a  town,  or  to  stones,  trees, 
permanent  features,  or  these  failing,  to  solidly  driven  stakes  and 
dug  pits,  so  that  it  could  be  accurately  relocated  if  the  point 
should  be  lost.  This  can  be  done  by  taking  the  angles  and 
bearings  of  the  reference  points  and  measuring  their  distances) . 
Let  the  chainmen  measure  the  distance  AB;  they  may  be  lined 
in  with  transit  if  desired,  but  usually  in  preliminary  surveys  the 


TAKING   PRELIMINARY  TRAVERSE 


35 


rear  chainman  can  do  this  by  eye  with  sufficient  accuracy;  the 
axmen  drive  stakes  properly  marked  at  each  station.  The 
transit  man  will  keep  the  notes  as  shown  in  Fig.  17. 

Move  the  instrument  to  B;  see  that  back  flagman  sets 
his  flagstaff  or  ranging  pole  on  the  point  A ;  with  the  vernier  at 
0  reverse  the  telescope  on  its  horizontal  axis  and  sight  on  back 
flag  at  A;  check  the  magnetic  bearing  of  A B.  Meantime  the 
front  flagman  goes  forward  and  sets  his  flag  at  a  place  previously 


s    i 


105 
100 

90 
85 
80 
75 
70 

s^ 

,.  

^ 

^ 

"X^ 

'  -      -v 

t^^ 

SK 

> 

' 

* 

N 

/ 

\f 

01         2345678        9       10      11       12      13      14      15      16 

FIG.  16. — Map  and  Profile  of  Surveyed  Road 

decided  upon  from  which  he  can  easily  see  the  instrument  and 
in  the  direction  wished  to  go  next.  Clamp  the  vernier  on  0 
and  bring  the  telescope  to  bear  on  the  back  flag;  reverse  the 
telescope  and  sight  on  the  front  flag;  read  the  angle  B'BC; 
repeat  the  operation  by  clamping  the  vernier,  loosening  the 
lower  motion  and  again  reversing  and  sighting  on  the  back  flag; 
reverse  and  sight  on  front  flag;  the  angle  should  now  read 
double  the  first  reading.  Get  the  magnetic  bearing  of  BC 
as  a  check  on  the  angle.  Chain  BC  and  proceed  to  the  next 
point  C. 


36 


ROAD  LOCATION 


If  a  straight  line  is  to  be  produced  double  sighting  should  be 
employed.  This  is  done  by  sighting  on  the  back  flag;  reverse 
the  telescope  on  the  horizontal  axis;  and  set  a  range  pole; 
unclamp  the  upper  motion  bring  the  telescope  to  bear  on  the 
back  flag  by  reversing  about  the  vertical  axis;  reverse  and 
again  set  the  pole.  The  true  prolongation  is  half  way  between 
the  two  positions  of  the  pole.  Drive  a  hub  there  and  repeat 
the  operation  with  the  range  pole  on  the  hub.  Bisect  the  two 


FIG.  17. — Sample  Page  of  Transit  Bote-book. 

positions  of  the  pole  point  and  drive  a  tack  over  which  to  set 
the  instrument  for  a  continuation  of  the  line. 

Head  Chainman. — After  setting  a  stake  and,  if  final  location, 
testing  it  the  head  chainman  must  walk  out  briskly  and  be 
ready  for  the  "  halt  "  command  as  he  reaches  the  next  station. 
He  should  practice  turning  and  walking  in  the  direct  line, 
occasionally,  to  assist  him,  sighting  back  over  the  two  stakes 
behind;  thus  much  time  will  be  saved.  In  breaking  chain  on 
steep  slopes  it  is  generally  best  for  the  head  chainman  to  pull 
out  the  entire  chain  and  then  come  back  to  the  necessary  point 


CHAINING  AND  STAKING  •  37 

to  break;  holding  the  tape  at  this  point  with  the  help  of  a  plumb- 
bob  or  the  pole,  he  draws  the  chain  taut  in  a  horizontal  plane; 
the  rear  chainman  comes  up  to  the  point  of  breaking  and  the 
head  chainman  goes  on  to  break  again  if  necessary.  An  axman 
or  flagman  standing  off  to  one  side  can  aid  in  getting  the  tape 
level. 

Rear  Chainman. — The  rear  chainman  follows  with  the  rear 
end  of  the  tape,  either  holding  it  or  following  as  it  is  being 
dragged  along  by  the  head  chainman.  He  should  see  that  the 
tape  does  not  disturb  the  transit.  He  should  see  that  it  does  not 
catch  in  rocks  or  bushes.  He  should  walk  and  stand  so  as  not 
to  obscure  the  line  of  vision  of  the  transit  man.  As  he  nears  the 
stake  last  set,  he  calls  a  halt,  holds  the  tape  at  the  stake  while 
the  head  chainman  straightens  it  out  and  gets  exact  distance  and 
direction.  The  rear  chainman  is  responsible  for  the  doing  up 
and  safeguarding  of  the  tape.  As  a  rule  pluses  should  be  read 
by  the  rear  chainman.  He  should  keep  a  record  of  pluses  and 
topographic  features  when  the  transit  man  is  not  at  hand. 
He  should  note  that  the  station  numbering  is  correct;  as  he 
reaches  a  stake  he  calls  its  number;  the  stakeman  imme- 
diately calls  the  number  of  the  stake  he  has  just  marked. 

Stakeman. — Stakes  are  usually  made  up  beforehand  and  a 
supply  carried  by  the  stakeman  in  a  sack.     Flat  stakes  are  used 
for  line  and  square  stakes  for 
hubs.     The  stakeman  should 
keep  up  with  the  head  chain- 
man and  be  ready  with  mark- 
ing crayon  or  keel  to  number 
the  stake  as  soon  as  he  hears 
the  rear  chainman  call  the 
number  of  the  last  stake;  or 

the  stakes  may  be  numbered 

, .   j  .     ,        ,,        e       FIG.  18.— Method  of  Marking  and 
ahead  and  tied  in  bundles  of  getting  stakeg 

ten  to  be  deposited  as  called 

for.  This  furnishes  a  check  on  the  numbering.  The  stake- 
man should  assist  in  clearing  the  line  and  is  under  the  direction 
of  the  head  chainman. 


38  ROAD  LOCATION 

Axman. — The  axman  carries  an  ax,  tacks,  and  if  desired 
an  extra  sack  of  stakes.  He  drives  stakes,  removes  under- 
brush and  other  obstacles  from  the  line  of  sight  and  the  instru- 
ment station.  In  this  work  care  must  be  taken  to  keep  on  the 
line  and  cut  only  as  much  as  may  be  necessary  that  there  may  be 
no  waste  of  time.  Other  members  of  the  party  of  course,  may 
assist  in  this  work  when  not  otherwise  engaged.  Line  stakes 
should  be  driven  crosswise  of  the  line  with  the  numbered  face 
to  the  rear.  Hubs  are  driven  almost  flush  and  witnessed  by  a 
flat  guard  stake  driven  about  10  inches  to  the  left,  marked  face 
slanting  toward  the  hub. 

Front  Flagman. — The  front  flagman  goes  ahead  and  under 
the  direction  of  the  chief  and  transit  man  establishes  hub  points. 
When  he  reaches  a  point  for  a  hub  he  signals  the  transit  man 
by  holding  his  pole  horizontally  above  his  head.  In  establishing 
these  points  he  should  not  only  go  in  the  general  direction  the 
line  is  to  follow,  but  should  select  positions  at  proper  distances 
from  the  transit  and  such  that  clearing  for  visibility  will  be  a 
minimum  for  both  fore  and  back  sight.  He  carries  with  him 
a  small  supply  of  hubs,  a  hand-ax,  tacks  and  large  nails.  Having 
selected  his  point  if  it  is  not  the  prolongation  of  the  original 
line,  he  drives  his  hub  and  sets  the  tack,  then  lets  the  transit 
man  get  the  angle.  If  it  is  a  prolongation  or  a  location  point 
he  must  let  the  transit  man  line  him  in.  He  must  watch  the 
transit  man  and  be  ready  instantly  to  plumb  the  pole  which  has 
its  spike  on  the  tack  head  by  standing  squarely  behind  it  and 
holding  it  lightly  with  the  tips  of  the  fingers  of  both  hands. 
When  the  head  chainman  is  called  back  for  other  work  he  may 
plant  his  pole  directly  behind  the  hub.  When  crossing  fences  a 
piece  of  cloth  tied  to  the  wire  or  nailed  to  the  top  board  will  act 
as  a  check  sight. 

Rear  Flagman. — The  rear  flagman -holds  a  sight  rod  on  the 
last  instrument  point  behind  that  where  the  instrument  is  set  up, 
for  back  sight.  He  records  in  a  memorandum  book,  kept  for 
that  purpose,  the  numbers  of  the  stations  on  which  he  gives 
back  sight.  If  materials  are  at  hand  he  may  cut  small  sap- 
lings and  set  them  behind  the  hub  when  signaled  ahead.  Split- 


AXMAN,    FLAGMAN.     LEVEL  PARTY 


39 


ting  the  tops  and  putting  a  small  piece  of  paper  in  the  split  to 
make  a  "  butterfly  "  renders  them  more  visible  and  such  pickets 
are  frequently  an  aid  to  the  transit  man  and  chief  in  forming 
conclusions  when  looking  back  over  the  line. 

Level  Party. — The  party  consists  of  two  members,  the  lev- 
eler  and  rodman,  to  which  may  be  added  an  axman  where 
necessary.  They  get  the  elevations  of  the  stations  and  suf- 
ficient other  points  to  make  a  profile  or  vertical  section  of  the 


/• 

Sla. 

B.S. 

F.S. 

H.I. 

Rod 

Eleu. 

^\ 

8.  Af.(l) 

0.70 

100.70 

Cioo.oo) 

Water  Tt 

ble,  N. 

£.  Cor.  I 

rich  Ho 

se 

0 

11.1 

89.6 

T.P.    Q 

0.52 

11.11 

90.11 

^89^59) 

Top  of 

Stake  5 

ta.  0 

1 

6.9 

83.2 

T.  P.    O 

0.27 

11.76 

78.  C2 

^TsTsT) 

Root  of 

Large  C 
Right  o 

ottonwo 
t  Koaau 

od  Tree 
ay 

2 

3.0 

75.6 

2+40 

6.2 

72.4 

Left  Ed 

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ter 
ut 

2+55 

6.2 

72  4 

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lian  Ch. 

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eep 

3 

39 

74.7 

T.P.    Q 

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89-17 

^77.  WT) 

4 

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82  5 

5 

1.9 

87  3 

5+40 

1.1 

as.i 

Top    < 

f  Hill 

6 

2.3 

86  9 

.7 

60 

83.2 

7+60 

3.1 

86.1 

T.P.    O 

3.04 

^selT) 

Top    Oj 

f  West  1 

Jail 

V 

12.86 

26.73 

J 

FIG.  19.— Sample  Page  of  Level  Notes. 

line.     They  follow  the  transit  party  and  should  be  on  the  alert 
to  catch  any  errors  that  may  have  occurred. 

A  bench  mark  is  a  point  selected  or  established  for  per- 
manent reference.  A  turning  point  is  a  temporary  reference 
point.  A  back  sight  is  a  rod  reading  taken  to  determine  the 
height  of  the  instrument  above  a  bench  mark  and  above  the  datum 
plane.  Afore  sight  is  a  rod  reading  to  determine  the  height  of  a 
point.  In  profile  leveling  back  sights  are  upon  established 


40  ROAD   LOCATION 

bench  marks  and  turning  points,  fore  sights  on  stations  and 
points  selected  for  turning  points  and  bench  marks.  It  is  well 
to  note  that  fore  sights  on  stations  not  turning  points  or  bench 
marks  are  termed  intermediate  sights.  For  profile  work  it  is 
preferable  to  use  a  combination  self  reading  and  target  rod,  the 
one  known  as  "  Philadelphia  "  is  a  favorite.  This  allows  the 
instrument  man  to  read  and  record  intermediate  sights  to  the 
nearest  tenth  of  a  foot,  turning  points  to  the  nearest  hun- 
dredth and  bench  marks  by  the  aid  of  the  target  to  the  nearest 
thousandth.  The  note  book  used  is  the  standard  "  level 
book  "  ruled  for  six  columns  on  the  left-hand  page  and  blank 
or  ruled  into  squares,  rectangles  or  columns  on  the  right-hand 
page.  (See  Fig.  19.) 

Operation. — The  level  man  sets  up  his  instrument  at  a  con- 
venient place  where  he  can  see  four  or  five  stations  either  way; 
lengths  of  fore  and  back  sights  should  be  approximately  the 
same  in  order  to  equalize  errors.  Take  a  back  sight  on  the 
estabEshed  bench  mark,  the  location  and  elevation  of  which 
should  be  fully  set  forth,  and  record  the  reading  in  the  second 
column  marked  B.  S.,  add  this  to  the  elevation  of  the  bench 
mark  to  get  the  height  of  the  instrument,  and  record  in  the 
fourth  column  marked  H.  I.  Take  a  reading  on  station  0  to 
the  nearest  tenth  of  an  inch  and  record  the  same  in  column 
five  under  heading  "  Rod."  This  is  an  intermediate  sight  but 
the  calculations  are  exactly  as  for  fore  sights;  subtract  the  rod 
reading  from  the  B.  M.  elevation  to  get  the  elevation  of  the 
station.  And  so  on  until  it  .is  necessary  to  move  the  instru- 
ment forward  when  a  turning  point  must  be  established.  This 
may  be  a  stake  or  boulder  or  other  point  sufficiently  solid  and 
determinate  to  repeat  the  reading  if  necessary.  Take  a  fore 
sight  on  the  T.  P.  and  record  the  rod  reading  to  the  nearest 
hundredth  in  the  third  column  under  F.  S.,  subtract  from  H.  I. 
for  the  elevation  of  T.  P.  Move  the  instrument  and  take  a 
back  sight  on  T.  P.  and  record;  add  this  to  the  elevation  for 
the  new  H.I.;  continue  to  the  end  of  the  survey.  As  a  check 
find  the  sum  of  the  back  sights  and  the  fore  sights  separately. 
Take  their  difference  or  algebraic  sum  considering  back  sights, 


OPERATION  OF  LEVELING  41 

which  are  additive,  positive  and  fore  sights,  which  are  sub- 
tractive,  negative;  this  difference  algebraically  added  to 
the  elevation  at  the  bench  mark  should  equal  the  elevation  of 
the  last  turning  point,  or  stated  another  way,  the  arithmetic 
difference  in  the  sums  of  back  and  fore  sights  over  any  portion 
of  the  line  equals  the  difference  in  elevation  of  the  ends  of  this 
portion,  remembering  that  the  first  sight  is  a  back  sight  and 
the  last  a  fore  sight.  Expressed  algebraically: 

S  =  Elevation  y  -elevation  x. 

It  is  better,  however,  to  use  only  turning  point  and  bench 
mark  rod  readings  in  checking  a  page,  comparing  the  differ- 
ence of  their  summation  with  the  difference  of  the  elevations 
or  heights  of  instrument  of  first  and  last  on  that  page.  Per- 
manent bench  marks  should  be  established  about  every  quarter 
of  a  mile.  These  should  be  upon  something  that  is  likely  to  be 
permanent  and  not  disturbed  during  the  process  of  construc- 
tion; the  water  table  of  a  building,  a  large  spike  driven  into  a 
telephone  post  or  a  tree  or  a  flat  rock,  all  of  which  can  be 
definitely  determined  and  recorded.  If  the  target  is  used  on 
turning  points  the  leveler  will  first  read  the  rod  and  make  a 
temporary  note  of  the  reading,  then  signal  for  the  target.  After 
this  is  set  and  clamped  the  rod  should  be  again  set  up  and  waved 
back  and  forth.  It  is  correctly  set  if  the  center  in  the  process  of 
waving  just  comes  up  to  the  cross  hair  and  then  recedes.  The 
rod  man  will  read  and  inform  the  leveler.  He  compares  the 
reading  with  his  check  reading  and  if  sufficiently  close  makes 
the  record. 

Rodman. — The  rodman  holds  his  rod  on  the  points  whose 
elevation  is  to  be  determined,  which  will  be  all  stations  and 
enough  intermediate  points  to  make  a  profile  on  a  scale  of 
40  to  100  feet  per  inch  horizontal  and  10  to  20  feet  per  inch 
vertical  (Plate  A,  profile  paper).  Elevations  may,  therefore, 
be  plotted  to  the  nearest  tenth  of  a  foot  and  horizontal  distances 
about  5  feet.  Observations  closer  than  this  will  not  only  not  be 
necessary  but  will  be  a  waste  of  time.  The  rodman  should 


42  ROAD  LOCATION 

select  determinable  positions  for  turning  points  and  bench 
marks.  Should  hold  his  rod  plumb,  which  can  best  be  accom- 
plished by  standing  directly  behind  it  and  holding  it  lightly 
with  the  fingers  of  both  hands.  In  taking  turning  points  and 
bench  marks  he  should  gently  wave  the  rod.  The  rod  man  will 
keep  a  "  peg  book "  and  record  turning  points  and  make 
the  necessary  calculations,  thus  checking  the  leveler.  He  will 
assist  the  leveler  in  plotting  his  notes,  and  check  the  compu- 
tations of  the  level  book. 

Topographer. — As  the  preliminary  survey  is  of. a  zone  the 
topographical  features  should  be  delineated  upon  the  map  in 
order  that  a  location  can  be  intelligently  projected.  The  topog- 
rapher, in  the  language  of  S.  Whinery,  "  must  possess  a  keen 
eye  and  a  good  judgment  for  locality,  distance  and  elevation.  .  . . 
Particularly  must  he  have  the  ability,  natural  or  acquired, 
from  experience  to  judge  of  the  relative  importance  of  the 
topography  he  sketches.  He  must  know  at  a  glance  from  the 
general  lay  of  the  country  that  the  final  location  will  hug 
this  hillside  closely,  and  its  topography,  therefore,  must  be 
taken  accurately,  while  the  other  will  not  be  touched,  and 
therefore  may  be  sketched  with  less  care." 

The  topographer  may  have  a  tape  man  to  assist  in  getting 
distances  or  he  may  work  alone,  stepping  off  distances  and 
getting  elevations  with  a  hand  level  held  at  the  known  height 
of  his  eye. 

His  note  book  (or  pad)  should  be  ruled  in  squares  like 
ordinary  cross-section  paper,  the  center  line  of  the  page  being 
the  traverse  line.  Topography  should  be  taken  for  about  300 
feet  each  side  and  contours  and  other  features  plotted  in  the 
field  where  everything  is  under  the  eye. 

The  topographer  works  about  a  day  behind  the  leveler  and 
should  take  from  the  level  book  the  elevations  of  the  several 
stations,  these  he  will  write  along  one  edge  of  his  book  (Fig.  20), 
numbering  the  stations  along  the  other.  With  the  elevation  of 
the  stations  known  and  the  hand  level  he  can  determine  con- 
tour elevations  on  each  side  of  the  station  at  convenient  dis- 
tances along  the  line  and  sketch  in  connections  as  he  goes  along. 


TOPOGRAPHER.     DRAFTSMAN 


43 


These  will  be  permanently  transferred  to  the  map  by  the 
draftsman  later. 

Draftsman. — The  number  of  maps  required  for  any  road 
will,  of  course,  vary  with  the  importance  of  the  scheme.  The 
following  will  be,  perhaps,  more  than  sufficient.  A  compre- 
hensive map  of  the  entire  project,  which  may  be  as  small  as 
1000  feet  to  the  inch. 


FIG.  20. — Sample  Page  of  Topography  Note-book. 

A  detail  or  working  map  on  a  scale  of  40  to  100  feet  per  inch. 

Profiles  of  preliminary  lines  platted  by  the  leveler  to  a  scale  of 
40  to  100  feet  per  inch  horizontal  and  10  to  20  feet  per  inch  vertical. 

Profiles  of  projected  locations  with  tracings  and  estimates  of 
quantities. 

Maps  and  profiles  of  final  location,  if  not  previously  shown. 

The  comprehensive  map  is  compiled  from  the  best  local 
map  at  hand.  The  maps  of  the  U.  S.  Geological  Survey  when 


44  ROAD  LOCATION 

available  are  valuable  as  they  give  contours  and  frequently 
character  of  soil,  condition  as  to  woodlands,  etc.  These  maps 
may  be  obtained  from  the  government  at  a  low  price  and  in 
sufficient  quantities  to  preclude,  frequently,  the  making  of 
other  maps — details  being  drawn  in  upon  them.  A  tracing 
may  then  be  made,  if  duplications  are  required.  The  detail 
map  shows  contours  for  each  5  feet  and  from  it  a  road  may,  if 
desired,  be  accurately  fitted  to  the  ground  surface. 

Several  methods  of  platting  a  traverse  survey  are  in  vogue. 
In  one  the  transit  line  is  laid  down  to  scale  and  the  deflection 
angles  turned  by  means  of  a  protractor.  This  may  do  for 
rough  quick  work  but  is  not  particularly  accurate  unless  a  pro- 
tractor with  vernier  attachment  is  at  hand.  Even  then  any 
error  tends  to  accumulate. 

Another  method,  which  is  similar  to  this  and  offers  much 


FIG.  21. 

the  same  objections  is  to  turn  the  angles  by  means  of  tangents. 
Here  is  measured  out  beyond  the  intersection  point  on  the  last 
line  drawn,  AB,  Fig.  21,  some  definite  distance,  say  10',  to  M. 
From  M  is  measured  on  the  perpendicular  to  right  or  left, 
MN=BM  times  the  tangent  of  the  deflection  angle.  This 
determines  a  point,  N,  through  which  the  next  section  of  the 
traverse  line,  BC,  is  to  be  drawn. 

The  method  of  platting  by  latitudes  and  departures,  coor- 
dinate method,  avoids  the  carrying  through  of  accumulative 
error.  The  method  is  somewhat  longer,  hence  more  expensive 
than  the  others;  but  is  theoretically  perfect.  A  base  line  is 
taken  parallel  to  the  edge  of  the  paper.  If  the  draftsman  uses 
judgment  in  the  selection  of  the  base  line,  he  may  be  able  to 
get  all  the  map  on  the  paper  without  making  breaks*  in  it. 


PLATTING  TRAVERSE  AND   PROFILE 


45 


MN,  Fig.  22,  is  the  base  line  and  MA,  the  tangent  along 
that  line.  The  angles  afiyd  are  calculated.  The  abscissa  or 
departure  HB  =  AB  cos  a,  the  ordinate  HA  =  AB  sin  a,  the 
point  B  is'  located  and  AB  platted.  Similarly  BJ=BC  cos 
|8  and  CJ  =  BC  sin  0.  If  the  signs  of  the  angles  be  taken  into 
account,  the  summations  of  the  departures  and  the  latitudes  will 
equal  the  total  departure  and  the  total  latitude  from  the  begin- 
ning point.  The  northernmost  side  of  the  map  should  be  the 
top. 

Profile. — For  a  small  project  the  profile  may  be  platted  on 
the  bottom  of  the  same  sheet  upon  which  the  map  is  drawn. 
For  more  extensive  projects  regular  profile  paper  should  be 
provided,  as  the  labor  of  platting  is  thereby  much  simplified, 


M    A 


FIG.  22. 


and  if  on  a  separate  sheet  it  can  be  shifted  along  from  place  to 
place  for  study.  See  Fig.  16. 

The  stations  are  marked  off  along  the  lower  margin,  in  the 
same  direction  as  on  the  map.  These  will  not  be  on  vertical 
lines  below  the  stations  on  the  map.  A  line,  freehand  or  straight 
segments,  drawn  through  the  plotted  points,  gives  the  profile 
of  the  ground  surface. 

The  elevations  are  plotted  above  their  respective  stations, 
care  being  taken  that  the  scale  is  such  that  all  points  fall  above 
the  lower  margin  of  the  profile  plot.  The  horizontal  scale 
should  be  the  same  as  the  scale  of  the  detail  map,  but  the 
vertical  scale  is  magnified  and  is  usually  made  5,  10  or  20  feet 
per  inch.  The  profile  should  show  the  location  and  elevations 
of  culverts,  bridges,  car  rails  at  crossings  or  adjacent  to  the  line, 
curbs,  and  other  objects  that  may  be  of  use  in  final  location. 


46  ROAD  LOCATION 

Topographical  Map. — The  detail  map  upon  which  the  tra- 
verse has  been  drawn  should  be  filled  in  from  the  notes  of  the 
topographer.  Of  especial  importance  are  the  contour  lines. 

ESTABLISHING  GRADE  LINE 

Having  the  maps  thus  far  completed  a  temporary  grade  line 
should  be  laid  down  on  the  profile.  A  black  silk  thread  or  the 
edge  of  a  transparent  triangle  will  be  of  assistance  in  balancing 
cuts  and  fills.  For,  while  the  finished  road  must  conform  as 
near  as  may  be  with  the  surface  of  the  land,  necessary  cuts 
and  fills  should  be  made  to. balance,  or  if  this  cannot  be 
done  the  fill  should  be  slightly  in  excess  as  the  extra  earth 
may  usually  be  obtained  from  the  side  of  the  road  thus  avoid- 
ing overhaul.  By  comparing  .the  contour  map  and  the  profile, 
a  line  may  be  projected  with  least  grades  and  least  grading. 
A  compromise  must  usually  be  made  between  directness  and 
grades.  If  the  ruling  grade  is  4  per  cent,  that  is,  a  rise  or  fall 
of  4  feet  in  a  100,  or  1  foot  in  25,  set  the  dividers  with  the 
points  exactly  25  feet  apart,  measured  on  the  scale  of  the  con- 
tour map,  if  the  contours  are  drawn  in  for  each  foot  of  elevation. 
Then  it  is  only  necessary  to  note  that  the  projected  line  shall 
not  be  shorter  than  the  distance  set  between  any  two  consecu- 
tive contours.  Stepping  over  the  contour  map  in  this  manner, 
several  tentative  lines  may  usually  be  run  between  controlling 
points.  This  line  is  made  up  of  a  succession  of  tangents  and 
curves;  each  point  of  curvature  (P.  C.)  and  point  of  tangency 
(P.  T.)  should  be  marked  as  well  as  centers  of  curves,  degree  of 
curvature,  and  angle  turned.  Profiles  should  be  drawn  for 
these  lines,  by  interpolating  elevations  from  the  contour 
map. 

The  grade  lines  having  been  laid  down  on  these  profiles, 
two  or  three,  may  be  selected  "  as  the  best  probable  loca- 
tion." With  a  table  of  quantities  for  level  cross-sections, 
estimates  for  cut  and  fill  will  be  made  and  routes  eliminated 
until  a  single  line  best  adapted  to  the  local  conditions  decided 
upon. 


ESTABLISHING   GRADE   LINE 


47 


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EARTHWORK  COMPUTATION 


40 


Crown  Corrections. — The  quantities  in  Tables  III  and  IV 
were  computed  for  trapezoidal  sections,  (Fig.  23.)  To  get  the 
true  cross-section  there  should  be  added  to  the  fill  and  subtracted 
from  the  cut  the  area  of  the  crown.  When  the  slope  is  given  in 

the  ratio  1  :  n,  c  :  J6  =  l  :  ny  that  is  c  =  — ,  therefore  the  area  of 


(6)  Excavation  or  Cut 


(  c  )  Crown  with  Slope  of  1 :  n 

FIG.  23. — Cross-section  in  Fill  and  Cut  Showing  Addition  and  Subtraction 
of  the  Crown  Necessary  for  Complete  End  Area. 

b2 
the  crown  triangle,  ABC,  equals  J6c= j-.     The  volume  of  a 

prism  I  feet  long,  with  breadth  of  base,  b,  expressed  in  cubic 
yards  is 

b2l 
V    108n 


50 


ROAD  LOCATION 


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II 


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a         fe         fe         fe         fc 

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—  |              rH              rH              ^              i^ 

CROWN   CORRECTIONS  51 

Table  V  gives  the  corrections  to  be  used  with  the  tables 
for  the  more  common  crowns.  Since  cuts  and  fills  very  nearly 
balance  each  other  this  refinement  will  ordinarily  not  be  neces- 
sary. This  table  can,  however,  be  used  in  the  final  calculations 
of  the  quantities,  if  the  crown  has  not  already  been  taken  into 
account. 

LOCATION 

The  line  of  the  selected  route  should  be  inked  upon  the  map 
and  then  located  upon  the  ground.  The  stakes  of  the  located 
line  will  all  be  marked  L  and  are  of  a  more  permanent  nature 

\ 


\ 


FIG.  24. 

and  more  accurately  set  than  those  of  the  preliminary  survey. 
In  projecting  the  "  paper  location  "  upon  the  ground,  it  must 
not  be  thought  that  it  will  "  fit  "  exactly.  Numerous  changes 
will  be  necessary.  The  preliminary  traverse  line,  already 
staked  out,  is  the  base  line  and  measurements  scaled  off  the 
map  are  made  with  reference  to  it  and  not  to  the  final  location. 

For  example  distances  BB',  DD' ',  GG',  etc.,  are  at  right 
angles  to  the  preliminary.  Several  points  along  a  tangent 
A,  B',  C,  D',  E,  F,  should  be  located  on  the  ground  from  the 
scaled  distances.  These  points  will  not  usually  be  found  in  an 
exact  straight  line,  so  the  line  staked  out  must  be  an  average  of 
these,  of  course,  taking  into  account  controlling  local  condi- 
tions. 

In  order  to  locate  this  finally  accepted  line  on  the  ground 
or  even  to  do  the  necessary  preliminary  surveying,  a  knowledge 


52 


ROAD  LOCATION 


of  curve  surveying  will  be  required.  Likewise  the  surveyor 
should  know  how  to  keep  his  instruments  in  adjustment.  Brief 
discussions  of  these  subjects  follow: 

CURVES 

Circular  curves  are  usually  employed  to  unite  straight 
reaches,  or  tangents,  of  the  road. 

A  simple  curve  is  the  arc  of  a  circle;  a  compound  curve  is  a 
combination  of  two  simple  curves  of  different  radii  on  the 
same  side  of  a  common  tangent.  A  reversed  curve  is  a  com- 

bination of  two  curves 
with  centers  on  opposite 
sides  of  a  common  tan- 
gent. 

In  Fig.  25,  ACB  is 
a  simple  curve  uniting 
the  tangents  EAD  and 
DBF.  The  angle  GDB 
is  the  intersection  angle 
usually  denoted  by  7;  it 
is  equal  to  the  central 
angle  AOB.  If  the  sta- 
tioning on  the  line  is 
from  A  toward  B  then  A  is  called  the  P.  C.,  point  of 
curve,  and  B  the  P.  T.,  point  of  tangent;  the  point  of  inter- 
sections of  the  tangents  the  P.  I.;  the  point  of  compound 
curve,  P.  C.  C.  (Fig.  26);  the  point  of  reversed  curve,  P.  R.  C. 
(Fig.  27.) 

By  geometry  and  trigonometry  a  number  of  formulas  may 
be  derived  for  the  properties  of  these  curves.  A  few,  only,  are 
given  below  for  simple  curves: 

Draw  the  broken  lines  DO  and  AB  (Fig.  25)  then  from  the 
right  triangles  thus  formed. 

AM=AOsm  AOM, 

,       ......     (1) 


Simpls 

FIG.  25. 


=  AD  =  AO  tan  AOM  =  R  tan  £7.          (2) 


PROPERTIES  OF "CURVES 


53 


The  degree  of  a  curve  is  defined  as  the  angle  which  an  arc 
of  100  feet  will  subtend  at  the  center.  If  this  angle  is  denoted 
by  D  and  s  is-  the  corresponding  arc  then, 

D 


18000 5729. 58 


Compound  Curve 

FIG.  26. 


Reserved  Curue 
FIG.  27. 


Since  there  is  no  easy  method  of  measuring  around  the 
curve,  measurement  is  made  by  unit  chords.  In  the  United 
States  the  unit  chord  is  100  feet.  Works  on  railroad  surveying 
define  the  degree  of  curvature  as  the  angle  at  the  center  sub- 
tended by  a  100-foot  chord.  The  radius  of  the  circle  deter- 
mined by  this  definition  would  be  (Equation  1) : 

T-V  -LV/vJ  **   /~\  t       T-N. 


2  sin  |D 

For  a  1°  curve,  therefore,  the  radius  is  5729.65,  while  by  the 
former  equation  it  is  5729.58.  It  is  customary  to  use  5730,  and 
since  R  varies  inversely  as  D  the  radius  of  any  other  curve  is 
found  from  that  of  the  l°-curve  by  dividing  by  the  degree  of 


54  ROAD  LOCATION 

curvature.  (This  rule  also  applies  for  long  chords,  tangents, 
externals,  mid-ordinates,  and  other  functions  of  the  curve 
which  depend  directly  upon  R  for  their  values.) 

The  error  incurred  by  using  chords  instead  of  the  actual 
length  of  the  arc  is  inconsiderable  providing  100-foot  chords 
are  used  on  curvatures  not  greater  than  7°,  50-foot  chords  from 
7  to  14°,  25-foot  chords  from  14  to  28°,  and  10-foot  chords  for 
larger  curvatures.  If  the  radius  does  not  exceed  100  feet  the 
curve  can  be  easily  struck  in  from  the  center. 

SIMPLE  CURVE  FORMULAS 

#  =  5730/Z>      . (1) 

#  =  50/sin  iD.  25 /sin  \D,  12.5/sin  JD,  5/sin  £>D,  for  chords 

of  100,  50,  25,  and  10  feet  respectively    ...     (2) 

R=Tcot%I         (3) 

r=#tanJJ (4) 

T=EcotlI         (5) 

E  =  R(sec$I-l) (6) 

E=T  tan  \I    .     . (7) 

Jf=fl(l-cosJ/)          ....     (8) 
M=Tcot  i/(l-cos  i/)    ...     (9) 

M=Ecos$I (10) 

S=1QQI/D         (11) 

S  =  27r#7/360 (12) 

C  =  2flsini/ (13) 

C  =  2Tcos|7 (14) 

C  =  2£sini//(seci/-l)     .     .  (15) 
If  the  long  chord  C  is  divided  by  a  point  into  two  parts,  si  and  82, 

the  ordinate  at  the  point  is,  m=~o'  TQQ*  TQQ'  D  (approximately). 

In  the  above  formulae  R  stands  for  radius  =  OA,  Fig.  25;  T  for  tan- 
gent, AD;  E  for  external,  DC:  M  for  mid-ordinate,  CM;  S  for  length 
of  arc,  ACB;  C  for  long  chord,  AB;  7,  inflection  angle;  D,  angle  sub- 
lending  a  chord  of  100  feet. 


LAYING   OUT   CURVES   WITH   TRANSIT  55 

LAYING  OUT  THE  CURVE 

With  Transit  and  Tape. — The  method  may  be  illustrated  by 
a  particular  case.  Suppose  there  are  two  tangents  meeting  at 
an  angle  of  70°  14'  to  be  united  by  a  simple  curve.  (Fig.  28.) 
The  P.  C.  may  be  arbitrarily  selected,  the  tangent  distance 
measured,  and  the  radius  and  degree  of  curvature  calculated  by 
Equations  (3)  and  (1).  Or  the  degree  of  curvature  may  be 
arbitrarily  selected  and  the  tangent  length  computed  by  (4) 
and  (1).  Suppose  the  latter  method  to  be  adopted  and  D  be 
taken  as  12°. 

"tan  35°  07' =  335.8. 


\ 


FIG.  28. 

The  chainmen  will  measure  or  count  back  this  distance  from 
the  intersection  point  and  set  a  stake  marking  it  P.  C.  (If 
the  P.  C.  has  been  chosen  arbitrarily  it  may  be  necessary  to 
measure  forward  and  set  P.  I.)  The  transit  is  set  up  at  P.  C. 
and  with  verniers  on  0°  directed  along  the  tangent  line  either 
by  sighting  at  (P.  I.)  or  to  a  backward  station.  It  is  not  likely 
that  P.  C.  will  fall  exactly  at  a  station  point;  suppose  it  to  be 
at  27+14.  Then  the  distance  to  the  first  station  on  the  curve 
will  be  36  feet.  This  is  sometimes  called  a  sub-chord.  Since 


56  ROAD   LOCATION 

the  degree  of  curvature  is  12,  the  length  of  chord  used  in  laying 
out  the  curve  should  be  50  feet,  and  this  will  subtend  an  angle 
at  the  center  of  JD  =  6°;  the  deflection  angle  for  a  chord  of 
50  feet  will  be  one-half  of  this  which  is  }D  =  3°.  The  sub- 
deflection,  therefore,  for  36  feet  will  be  |f  of  3°  =  2°  9.6'.  This 
angle  is  turned  off,  deflected,  on  the  transit  in  the  direction, 
right  or  left,  which  the  curve  is  to  take.  The  rear  chainman 
holds  36  feet  on  the  P.  C.,  the  transit  man  lines  in  the  head 
chainman  who  keeps  the  tape  taut.  The  point  being  located 
a  stake  is  marked  27+50  and  driven.  The  transit  man 
now  deflects  an  additional  angle  of  JZ>  =  3°,  making  the  total 
vernier  reading  now  5°  9.6' ;  this  is  the  index  angle  for  Station  28. 
A  stake  is  set  for  Station  28  with  a  full  50-foot  chord.  Suc- 
ceeding stations  are  set  in  the  same  manner,  deflecting  3°  for 
each  station.  If  it  becomes  necessary  to  move  the  transit, 
and  railroad  engineers  advise  this  when  the  index  angle  reaches 
15°  to  18°,  even  though  the  stations  are  visible,  the  transit  man 
will  signal  for  a  hub.  When  the  hub  is  checked  he  goes  for- 
ward and  sets  his  transit  on  it.  If  he  desires  to  get  the  tangent 
line  he  would  clamp  his  verniers  on  0°  and  sight  back  to  the 
P.  C.  then  deflect  the  index  angle  of  the  station  on  which  the 
instrument  is  now  setting.  Suppose  the  resetting  to  be  at 
station  30  then  the  index  angle  would  be 

2°9.6'-f-(5X30)  =  17°9.6'. 

The  telescope  is  now  plunged  and  it  points  along  the  tangent. 
Further  stationing  can  be  located  as  before.  Note  that  if  the 
tangent  line  is  not  required  the  transit  man  will  save  time  by 
deflecting  after  the  back  sight  the  index  angle  of  the  next  sta- 
tion, namely  20°  9.6'.  The  index  angle  is  always  the  sum  of 
the  deflection  angles  from  the  P.  C.  The  transit  notes  would  be 
kept  something  like  the  form  shown  on  page  57. 

The  transit  is  put  "  in  tangent  "  over  a  second  or  other  hub 
by  the  following  operations:  (1)  clamping  the  plates  upon  the 
index  angle  of  a  previous  hub  which  is  to  be  used  as  a  back  sight; 
(2)  backsighting  on  the  hub;  (3)  clamping  the  lower  and  loosen- 
ing the  upper  plate  and  deflecting  the  transit  until  the  index 


TRANSIT   NOTES 


57 


Remarks 

jjf  S  co 

O            II         II 

i-H     >*^   -^, 

Magnetic 
Course 

CO                                                                                       00 
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oooooooooooo 

COCO<N(N(Nc.Mt-ii—  ITH 

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CO           CO           CO           CO           <M           C<J                  (N 

58  ROAD  LOCATION 

angle  of  the  hub  over  which  it  now  stands  has  been  reached; 
(4)  plunging;  this  brings  the  telescope  in  line  with  the  tangent 
forward.  It  must  be  noticed  that  this  is  equivalent  to  turning 
off  from  the  chord  between  the  hubs  an  angle  equal  to  half 
the  subtended  central  angle.  To  apply  this  to  the  particular 
example  at  hand:  When  the  P.  T.  has  been  located,  a  hub  set, 
and  the  transit  moved  to  that  point,  it  is  clamped  on  17°  9.6', 
the  index  reading  for  station  30,  backsighted  and  deflected 
35°  .7',  the  index  reading  for  P.  T.  The  telescope  is  now 
directed  along  the  tangent  toward  P.  I.,  and  if  that  point  can 
be  seen  it  furnishes  a  check  upon  the  work. 

To  Locate  the  Curve  by  Chord  Offsets.  —  The  length  of  the 
mid-ordinate,  AB,  is  calculated  by  the  formula 

M  =  R(l-  cos  J7), 

or  by  the  approximate  formula 

r<2 

TJie  ordinates  of  other  points  are  given  by 

ab     7    o      b 


EXERCISE 


Suppose  I,  Fig.  29,  to  be  42°,  D  =  6°,  and  that  P.  C.  is  at  station  4+25. 
The  angle  A  then  would  be  75/100  of  6°  =4.5°  =4°  30'  and  the  angles 


i/-£i  =  21°-4°  30'  =  16°  30'. 
=  1Q°  30'  -6°  =10°  30'. 

BOE  =  10°  30'  -6°  =  4°  30'. 

and 

C7qn 

BA=R(l-cos  21°)  =-^p(l-.9336)  =63.4;  AJ  =  R  sin  21°  =  342.3; 


£P  =  #(l-cosl6°30')=39.7;  LM  =  63.4-39.7  =  23.7;  PL  =  tfsin  16°  30' 

=271.2;  JM  =  342.3  -271.  2=  --  ;  BQ  =  R(l-cos  10°  30'=  --  ; 
GF=—;    QG  =  RsmW°3&=  --  ;  SE=  --  ;  CE=  --  ; 
with  the  coordinates  of  the  curve  determined  it  may  be  readily  staked  out. 


LAYING   OUT  THE   CURVE   BY  OFFSETS 


59 


To  Locate  the  Curve  by  Tangent  Offsets. — The  angle  between 
the  tangent  at  P.  C.  and  the  chord  aci,  Fig.  30,  is  one-half  the 


P.L 


gv     *         ft        0\ 

*\    \ 

/ 

\    ^      \ 

/ 

\    *      \ 

/ 

\    \     \ 

\                 \       ___^t—  D2* 

/ 

/ 

«  ^V""^         *                | 

/ 

\^                \               1 

/ 

\ 

/ 

\       i       ! 

/ 

P. a 


central  angle  DI,  therefore  at\  =  ac\  cos  JZ>i;  similarly, 
-cos  J(Di+Z>),  etc.      Also,  /ici  =  aci    sin   }Di; 

,  etc.     But  aa  =  2R  sin  JDi;  ac2  =  2R  sin 


sn 


60  ROAD  LOCATION 

etc.  Therefore  at\  =  R  sin  1)\  at>2  =  li  sin  (Di  +  D),  etc.  And 
'tid  =  2R  sin2  |D,  £2c2  =  2rsin2  J(Z)i  +  D),  etc.  The  method  of 
procedure  is  clearly  to  measure  at\  then  turn  a  right  angle, 
either  with  transit  or  tape,  and  measure  t\c\.  The  method  is 
valuable  for  locating  stations  whose  view  from  P.  C.  is  ob- 
structed and  the  transit  deflection  cannot  be  used. 

The  tangent  offsets  could  have  been  calculated  by  the 
approximate  formula 

7/0*  \2n 

fc=8(ioo)  D' 

EXERCISE 

Find  six  offsets  to  a  4°-curve  at  points  50  feet  apart,  measured  around 
the  curve.  By  successive  applications  of  the  above  rule  the  offsets  are 
0.88,  3,50,  7.88,  14.00,  21.88,  and  31.50  feet. 

NOTE:  These  values  are  approximate  only  and  are  more  nearly  correct 
when  measured  toward  the  center  of  the  curve,  0,  but  when  the  degree  of 
curvature  is  small  and  the  offsets  are  short  the  error  is  not  great. 

Instead  of  measuring  the  offset  from  the  tangent  every  time,  the  second 
offset  may  be  measured. from  the  chord  through  a  and  c  produced.  In  this 
exercise  the  first  offset  from  the  tangent  will  be  as  before,  0.88  foot.  The 
second,  third,  fourth,  etc.,  will  be  double  that  or  1.66  feet.  An  0.88  foot 
offset  will  at  any  time  determine  the  tangent. 

Striking  in  the  Curve. — If  the  radius  of  curvature  is  100 
.  feet  or  less  and  the  center  if.  accessible  the  easiest  way  is  to  hold 
one  end  of  the  tape  at  the  center  and  with  the  desired  radius 
mark  as  many  points  on  the  curve  as  necessary. 

Locating  by  Eye. — Sometimes  a  short  curve  may  be  located 
by  sticking  pegs  or  marking  pins  along  its  course  and  by  looking 
over  them  determine  whether  or  not  the  curve  is  smooth. 
Where  a  record  of  the  survey  has  to  be  kept  other  methods 
should  be  employed. 

Parabolic  Curves. — Let  AEB,  Fig.  31,  be  a  parabola, 
AC  and  BC  its  tangents, '  A  B  the  chord  uniting  the  tangent 
points  and  D  the  mid-point  of  AB.  According  to  analytic 
geometry : 

(a)  CD  is  the  principal  axis  or  diameter  of  the  parabola  and 
the  curve  bisects  CD  in  E. 


PARABOLIC  AND  VERTICAL  CURVES 


61 


(6)  If  lines  are  drawn  from  points  t\,  fo,  £3  ...  on  the  tan- 
gent, parallel  to  the  diameter  CD,  the  tangent  offsets  t\m\,  tim<iy 
tsms  .  .  .,  are  proportional  to  the  square  of  the  distances 
A ti,  At2,  At%  .  .  .,  from  the  point  of  tangency  A. 

(c)  A  tangent  to  the  curve  at  the  extremity  of  a  middle 
ordinate,  as  at  E,  is  parallel  to  the  chord  of  that  ordinate,  AB. 


FIG.  31. 

These  properties  give  several  methods  for  laying  out  the 
curve.  For  example: 

Locate  D,  the  mid-point  of  AB',  locate  E,  the  mid-point 
of  CD',  then  any  tangent  offset  tm  :  CE::At2  :  AC2). 


Substituting  At,  AC  and  CE,  found  by  measurement  in  the 
formula  tm  is  determined  and  the  point  m  may  be  staked  out. 

Or,  draw  a  tangent  through  E,  suppose  it  meets  the  tangent 
through  A  at  t,  draw  the  chord  AE,  the  mid-point  of  tK  is  m, 
a  point  on  the  curve.  Continued  application  of  this  operation 
will  give  any  number  of  points.  After  the  curve  has  been 
determined  it  may  be  stationed  by  using  50-foot  chords  from  A. 

Vertical   Curves.  —  The   parabolic   curve   lends   itself  very 


62  ROAD  LOCATION 

readily  as  a  vertical  curve  for  rounding  out  the  intersection  of 
two  grade  lines.  If  gi=3  per  cent  is  the  gradient  of  AC,  and 
02=  —2  per  cent  is  the  gradient  of  CB  the  algebraic  difference 
is  the  change  in  grade  at  C;  gi—g2  =  3  —  (—2)  =  5  per  cent. 
Experience  shows  that  for  a  difference  of  less  than  3  per  cent,  a 
100-foot  curve,  50  feet  each  side  of  C,  will  be  ample  for  easy 
transition;  from  3  to  6  per  cent,  200  feet;  above  6  per  cent, 
300  feet.  In  this  example,  therefore,  200  feet  will  be  taken. 

Let  the  elevation  of  C  be  110,  then  the  elevation  of  A  will  be 
110-(3  per  cent  of  100)  =  107;  of  B,  108;  of  D,  (107+108) /2 
=  107.5;  of  E,  (107.5+110)/2=108.75.  Note  that  the 
elevation  of  E  is  taken  the  same  as  that  of  El,  the  mid-point 
of  CD. 

Divide  the  tangents  AC  and  BC  each  into  four  25-foot 
lengths  then  the  tangent  offset 


At 


and  the  grade  at  mi  is  the  grade  at  A+the  rise  in  At\—  the 
tangent  offset— 107 +.75 -.078  =107.67.  Similarly,  ^2w2  =  A 
(1.25)  =  .31,  grade  at  m2  =  108.19;  £3^3  =  9  (.078 125)  =  .703, 
grade  at  m=  108.54-;  in  general  the  offset  at  the  nth  station  from 
the  tangent  point  A  will  be  n2  times  the  offset  at  the  first  station. 
The  offsets  for  points  beyond  C  may  be  calculated  in  the  same 
manner  but  it  is  easier  to  notice  that  teniG^timi,  t*>m*>  =  t<2.m<2l, 
£4^4  =  237/13.  Thus  the  elevation  at  m^  =  elevation  at  C— the 
fall  in  C*-*m=110-.5-.703  =  108.8. 

If  the  line  station  should  fall  between  fa  and  fe,  say,  its  ele- 
vation could  be  found  by  the  offset  at  that  point  or  by  inter- 
polation. 

ADJUSTMENTS  OF  THE  TRANSIT  AND  LEVEL 

The  Important  Adjustments  of  the  Transit  Are. — (1)  To 
make  the  plane  of  the  plate  bubbles  perpendicular  to  the  ver- 
tical axis;  (2)  to  make  the  line  of  sight  (collimation)  perpen- 
dicular to  the  horizontal  axis;  (3)  to  make  the  horizontal  axis 


TRANSIT  ADJUSTMENTS  63 

perpendicular  to  the  vertical  axis;     (4)   to  make  the  attached 
level  and  line  of  collimation  parallel  to  each  other. 

1.  The  Plate  Bubble. — Unclamp  the  plates  and  level  the 
instrument  with  the  bubbles  on  line  with  the  two  pairs  of  leveling 
screws;  turn  the  instrument  half  way  around  (180°  in  azimuth). 
Half  the  apparent  error  is  the  real  error;  bring  the  bubble  half 
way  back  by  turning  the  small  nuts  at  the  ends  of  the  levels 
with  the  adjusting  pin.     Again  level  the  instrument  and  repeat 
the  operation  until  the  bubbles  will  remain  in  the  middle 
through  the  entire  revolution  of  the  instrument. 

2.  Line  of  Collimation. — Set  up  and  level  the  instrument; 
focus  on  some  well-defined  point;   clamp;   elevate  and  depress 
the  telescope  by  turning  about  its  horizontal  axis.     If  the  point 
does  not  appear  to  travel  along  the  vertical  wire,  the  ring 
screws  must  be  loosened  and  the  ring  turned  by  gently  tapping 
one  of  the  screw-heads  until  the  condition  is  fulfilled.     Tighten 
the  screws  and  test.     Now  direct  the  intersection  of  the  cross 
wires  on  an  object  200  or  300  feet  distant;    clamp;'  transit; 
set  a  point  in  the  line  of  sight  about  the  same  distance  in  the 
opposite  direction;    unclamp  and  turn  the  plates  in  azimuth 
half  way  around  and  direct  again  to  the  first  object;    transit 
and  set  another  point  beside  the  first.     The  two  points  should 
coincide;    correct  the  error  by  turning  the   capstan  headed 
screws,  loosening  one  and  tightening  the  other  thus  moving  the 
vertical  cross-hair  until  the  line  of  sight  has  been  moved  over 
a   distance  equal    to    one-fourth   the   apparent    error.      Test 
results. 

3.  The  Standards. — Set  up  and  level  the  transit;    sight  to 
some  high  point  as  the  top  of  a  house  or  spire;  lower  the  tele- 
scope and  set  a  point  in  line  of  sight  slightly  below  the  level  of 
the  instrument;    turn  the  instrument  half  around  in  azimuth; 
reverse  the  telescope  and  sight  on  the  lower  point;   clamp  and 
elevate  the  telescope  until  the  first  point  comes  into  view.     If 
the  wires  do  not  bisect  it  the  adjustment  necessary  is  made  by 
raising  or  lowering  one  end  of  the  horizontal  axis.     The  appar- 
ent error  is  double  the  actual  error.      The  final  adjustment 
should  be  made  by  a  right-handed  turn  of  the  adjusting  screw. 


64  ROAD  LOCATION 

Tighten  the  cap  screws  just  enough  to  take  up  all  looseness  in 
the  bearing.* 

4.  Attached  Level. — Construct  a  level  line  and  adjust  the 
instrument  to  agree  with  it  (see  adjustment  of  level,  page  65). 

The  Important  Adjustments  of  the  Y-Level  are:  (1)  To 
make  the  line  of  sight  coincide  with  the  axis  of  the  clips  or  par- 
arallel  to  it;  (2)  to  make  the  line  of  sight  and  the  bubble  tube 
parallel;  (3)  to  make  the  axis  of  the  bubble  tube  perpendicular 
to  the  vertical  axis  of  the  instrument. 

1.  Line   of  Collimation. — Make    the   horizontal   cross-hair 
level  by  turning  the  ring  until  the  cross-hair  coincides  with  a 
level  surface,  or,  as  the  telescope  is  turned  in  azimuth  a  point 
will  appear  to  travel  along  the  wire,  the  instrument  being  set  up 
as  nearly  level  as  possible.     Next  loosen  the  clips  by  removing 
the  Y-pins  clamp  the  instrument  on  the  leveling  head,  and  by 
the  leveling  and  tangent  screws  bring  the  wires  on  a  clearly 
marked  point;    carefully  rotate  the  telescope  in  its  Y's  one-half 
round  and  see  if  the  intersection  now  coincides  with  the  point. 
Correct  one-half  the  apparent  error  by  moving  the  cross-hair 
ring  by  means  of  the  capstan-head  screws.     Repeat  the  opera- 
tion if  necessary. 

2.  Level  Viol. — Clamp  the  instrument  over  a  pair  of  leveling 
screws  and  bring  the  bubble  to  the  middle  of  the  tube.    Rotate 
the  telescope  in  the  Y's  so  as  to  bring  the  bubble  tube  out  of 
vertical  with  the  telescope  axis.     Should  the  bubble  run  toward 
the  end  of  the  tube  it  shows  that  the  vertical  plane  passing 
through  the  axis  of  the  telescope  is  not  parallel  to  that  through 
the  axis  of  the  bubble.     Correct  the  error  by  means  of  the  cap- 
stan-head screws  on  each  side  of  the  viol  holder.     Test  the 
adjustment.     This  adjustment  is  preparatory  to  making  the 
level-tube  parallel  with  the  axis  of  the  Y's.      Bring  the  bubble 
to  the  middle  of  the  viol  with  the  leveling  screws;    without 
jarring  the  instrument  lift  the  telescope  out  and  reverse  it  in  the 
Y's.     Should  the  bubble  run  to  either  end  lower  that  end  or 
raise  the  opposite  end  until  half  the  error  is  corrected.     Level 
up  the  instrument  and  test. 

3.  The  Y's.— The  bubble  tube  must  now  be  set  at  right 


ADJUSTMENTS   OF   THE   LEVEL  65 

angles  to  the  axis  of  the  instrument.  Bring  the  bubble  to  the 
middle  of  the  tube  directly  over  a  pair  of  leveling  screws;  turn 
the  instrument  about  its  vertical  axis  180°.  If  the  bubble 
runs  to  one  end  of  the  tube  bring  it  half  way  back  by  the 
Y-nuts.  Test. 

The  Important  Adjustments  for  the  Dumpy  Level   are: 

(1)  To  make  the  bubble  line  perpendicular  to  the  vertical  axis; 

(2)  to  jnake  the  line  of  sight  parallel  to  the  bubble  line. 

1.  Bubble. — Bring  the  bubble  to  the  center  over  a  pair  of 
leveling  screws;   revolve  about  the  vertical  axis  through  180°. 
If  the  bubble  moves  bring  it  back  half  way  by  the  screws  at  the 
end  of  the  tube.     Test.     The  bubble  should  remain  in  the  mid- 
dle through  the  complete  revolution. 

2.  Line  of  Collimation. — Construct  a  level  line  by  driving 
two  pegs  at  equal  distances  in  opposite  directions  from  the 
instrument  and  taking  careful  reading  on  them  with  the  bubble 
in  the  middle  of  its  tube.     The  pegs  may  be  driven  to  the  same 
rod  reading  then  if  the  distances  are  equal  they  will  be  level. 
If  ground  cannot  be  found  for  this  the  difference  in  the  level 
of  the  two  pegs  must  be  taken  jnto  consideration.     Set  up  the 
instrument  so  near  one  peg  that  the  height  of  the  eye-piece 
can  be  measured  directly  by  holding  the  rod  vertically  on  the 
peg.     Sight  to  the  same  "  height  of  instrument  "  at  the  other 
peg  (or  at  the  calculated  height  of  instrument  if  the  pegs  are 
not  level).     The  axis  of  the  telescope  will  now  be  a  level  line. 
If  the  bubble  is  not  in  the  middle  of  its  tube,  bring  it  half  way 
to  the  middle  and  adjust  the  horizontal  cross-hair  to  the  "  height 
of  instrument  "  reading  at  the  farther  peg.     Test  by  repetitions. 

CROSS-SECTIONING 

Having  located  the  road  by  setting  the  center  line  stakes 
cross-sectioning  is  necessary.  By  cross-sectioning  is  here 
meant  the  several  combined  operations  of  (a)  taking  levels  of 
the  lay  of  the  land  at  right  angles  to  the  center  line  of  location, 
(6)  the  setting  of  marked  grade  and  slope  stakes,  and  (c)  the 
recording  of  the  notes  in  such  a  manner  that  the  true  shape  of 


66  ROAD   LOCATION 

the  area  of  a  transverse  section  of  the  road  at  that  place  may  be 
plotted  and  its  area  computed;  also,  from  the  stakes  set,  the 
road  may  be  constructed  in  true  form,  grade  and  position. 

Cross-sections  (transverse  sections)  are  taken  at  each  station 
and  at  intermediate  points  where  the  longitudinal  slope  changes, 
considerably. 

Slope  Stakes  are  set  to  mark  the  points  on  cross-sections 
where  the  side  slope  meets  the  ground  surface. 

Grade  Stake. — All  stakes  which  indicate  cuts  or  fills  are 
generally  known  as  grade  stakes.  The  term  is  sometimes,  in 
counterdistinction  to  slope  stakes,  used  to  indicate  a  stake  at 
a  station  on  the  center  line  of  location  on  which  has  been 
marked  the  cut  or  fill  at  that  station. 

Grade  Point. — A  point  in  the  intersection  of  the  plane  of 


,   .. 

-  Level  Culb       |  I 


p 

1         2 

i  i  i 

4 

l 

,  i  i 

j^LJ 

!    1    1 

~lo~~li  —  1 

.liln'illllHilllHillllii 

Iron  En 
Strap 

f 

Level 
FIG. 

Board 
32. 

the  roadbed  with  the  surface  of  the  ground.  Three  are  usually 
set  across  the  roadway;  they  are  driven  flush  with  the  ground 
and  witnessed  by  a  stake  bearing  the  inscription  0.  0.  The 
point  is  best  found  by  trial  such  that  the  rod  reading  equals  the 
difference  between  the  height  of  instrument  and  elevation  of 
grade. 

Leveling. — This  may  be  done  with  a  hand  level,  a  level- 
board,  or  the  Y-level.  When  the  hand  level  is  used,  the  height 
of  the  eye  of  the  observer  must  be  accurately  known  and  proper 
corrections  made  in  the  rod-reading.  A  staff,  of  such  length 
that  the  line  of  sight  of  the  hand  level  when  placed  on  top  of 
it  is  exactly  5  feet  from  the  ground,  may  be  used. 

With  the  Level  Board. — A  level  board  is  a  long  straight- 
edge, Fig.  32,  graduated  to  feet  and  inches  (12  feet  is  a  con- 
venient length),  made  of  light  straight-grained  lumber,  such  as 
white  pine,  spruce,  or  fir,  8  inches  wide  at  the  middle  and 


CROSS-SECTIONING  67 

tapered  to  4  inches  at  the  ends,  and  about  1|  inches  thick. 
Iron  straps  at  the  ends  will  prevent  wear  and  splitting.  A  few 
hand-holds,  cut  into  the  board,  will  be  found  convenient.  Two 
men  are  necessary  to  handle  a  level  board  efficiently.  It  is 
well  adapted  to  rough  country  where  the  slopes  are  such  that 
several  set-ups  of  the  Y-level  might  be  necessary  for  a  single 
cross-section. 

With  the  Y-level  cross-section  leveling  may  be  done  and  the 
center  line  elevations  taken  or  checked  at  the  same  time. 

Grade  stakes  are  set  for  the  convenience  of  the  "  grader." 
On  the  center  stake,  on  the  opposite  side  from  the  location  or 
station  number  is  marked  the  cut  or  fill  at  that  point  :  Thus 
C  4.2  means  a  cut  of  4.2  feet;  F  0.3  means  a  fill  of  0.3  feet. 


Height  of  Instrument 


FIG.  33. 

Slope  stakes  are  set  at  the  "  toe  of  the  slope  "  with  top  inclined 
inward  for  cuts  and  outward  for  fills,  and  marked  with  C  or  F 
followed  by  the  vertical  distance  to  the  grade  plane  of  the  road. 
Setting  Stakes. — The  slope  of  the  fill  and  cut  will  vary  with 
the  material  but  for  ordinary  earth  a  common  slope  for  fill  is  1 
vertical  to  1|  horizontal  and  cuts  1:1.  Referring  to  Fig.  33, 
having  obtained  the  elevation  of  the  center  stake,  say  98.4, 
just  as  in  leveling  for  the  preliminary  survey  the  grade  elevation 
which  has  previously  been  taken  off  the  profile  and  recorded 
is  looked  up,  suppose  it  to  be  95.2;  this  indicates  that  the 
ground  is  there  3.2  feet  higher  than  the  grade,  hence  the  stake 
is  marked  C  3.2.  Suppose  the  width  of  the  roadway  in  fill  to 
be  20  feet,  in  cut  to  be  24  feet,  the  extra  width  to  allow  for  side 
ditches.  If  the  H.  I.  at  this  time  is,  say,  105.3,  a  rod  on  grade 


68  ROAD  LOCATION 

at  this  station  would  read  H.  I.  -grade  =  105.3  -95.2=  10.1  = 
grade  rod  or  station  constant.  Since  upon  holding  the  rod  at 
the  edge  of  the  grade  the  reading  is  found  to  be  greater  than 
that,  it  will  be  necessary  to  fill  on  the  lower  side  of  this  cross- 
section.  The  rod  man  comes  back,  trying  at  various  places 
until  he  finds  a  place  the  reading  of  which  is  10.1  (grade  rod); 
a  stake  is  placed  here  and  marked  0.  0.,  that  is,  grade.  The 
rod  man  keeps  setting  his  rod  out  from  the  center  until  he  finds 
a  point  where  the  rod  reads,  10.1  (grade  reading)  -f-  (distance  - 
out  - 10)  X  H,  In  this  case  at  23.5  out  the  rod  reads  19.1.  The 
rod  man  and  leveler  will  compute  thus,  19.1  —10.1=9.0  (B.  C., 
Fig.  33),  one  and  one-half  times  9.0  =  9.0+4.5  =  13.5  (C.  D.): 
13.5-f  10  (half-width  of  road  bed)  =23.5  (AB).  So  that  the 
distance-out  and  the  road  reading  check.  A  stake  is  driven 
at  the  toe  of  the  slope  and  marked  F  9.0. 

Going  out  on  the  other  side  it  is  noticed  that  there  is  a 
marked  change  in  slope  8  feet  from  the  center.  A  rod  reading 
is  therefore  taken  at  this  point  and  the  cut  recorded,  but  no 
stake  driven.  Suppose  the  reading  here  to  be  2.1,  subtract 
this  from  the  "grade  rod"  (10.1-2.1  =  8.0)  and  the  cut  is 
seen  to  be  8.0.  Going  on  out,  suppose  a  trial'reading  is  made 
at  20  feet,  and  the  rod  reading  is  1.2.  The  computation  is 
10.1-1.2  =  8.9;  8.9+12  (half  width  of  road  in  cut)  =20.9; 
but  the  distance  out  is  20.0,  therefore,  another  trial  is  made 
farther  out,  say  22  feet  with  a  reading  of  0.7  feet,  10.1  -0.7  =  9.4 
(cut);  9.4X1  (slope) +  12  =  21. 4;  which  being  less  than  the 
distance  out,  22,  shows  the  distance  out  to  be  too  great.  A 
trial  is  then  made  farther  in,  say  at  21.0  and  a  rod  reading  of 
1.2;  10.1-1.2  =  8.9;  8.9+12  =  20.9,  which  agrees  well  enough 

with  the  distance-out  so  a  stake  is 
driven  here  and  marked  C  8.9. 

This   is  a   practical   method   of 
finding    slope    stake    positions    by 
trial.     A  course  of  reasoning  on  the 
FIG.  34.  part  of  the  rod  man,  similar  to  this 

might  be  followed  which  would  also 
be  mathematically   correct.     If  the  ground   were   level   the 


SETTING  SLOPE  STAKES  69 

distance-out  would  be  b-\-s\,  where  si~  g  tan  slope.  But  in 
going  out  this  distance  the  ground  has  risen  an  amount  1i2,  Fig. 
34,  add  therefore  to  the  distance-out,  82  =  /i2  tan  slope,  continue 
this  until  distance-out  and  change  in  height  are  inconsiderable, 
say  less  than  0.1  foot.  The  algebraic  equation  then  is 


.  .  .)  tan  slope. 

Some  engineers,  instead  of  marking  the  slope  stakes,  set 
grade  stakes  just  back  of  them,  F\,  Fig.  33,  having  an  even  or 
integral  cut  or  fill  and  an  integral  offset.  In  the  figure  the 
stake  is  shown  with  an  offset  of  22  feet  and  a  cut  of  10  feet. 
By  setting  another  stake  on  the  other  side  of  the  road,  say  with 
an  offset  of  25  feet  and  a  fill  of  10  feet,  a  string  may  be  attached 
to  the  top  of  the  upper  stake  and  held  at  the  required  height 
above  the  lower  one,  pulled  taut  and  measurements  made 
downward  from  it  to  the  road  surface.  A  small  allowance 
should  be  made  for  the  sag  in  the  string. 

Slope  stakes  may  be  set  by  using  a  level  plane,  DE,  Fig.  33, 
as  a  basis  through  the  edges  of  the  roadway,  or  a  plane  through 
the  crown,  or  one-half  way  between.  Whichever  plane  is  taken 
corrections  should  be  made  for  the  crowning  of  the  roadway  in 
the  marking  of  the  center  stake  and  in  calculating  the  quantities. 

In  practice  the  quantity  in  the  parentheses  is  guessed  at  and 
the  rod  reading  taken,  the  cut  (or  fill)  is  obtained  by  comparison 
with  the  grade  rod  of  the  station,  this  multiplied  by  the  slope 
tangent  (usually  1J  for  fill  and  1  for  cut),  and  added  to  half 
the  road  bed;  the  sum  is  then  compared  with  the  distance  out. 

RECORDING  CROSS-SECTION  NOTES 

An  ordinary  level  book  with  a  column  for  grade  elevations 
for  the  profile  record  of  the  center  line  of  stakes  is  suitable. 
The  right-hand  page,  Fig.  35,  can  be  used  for  cross-sections. 
In  the  middle  is  written  the  cut  (  +)  or  fill  (  —  )  at  the  center  stake, 
on  either  side  the  numerator  of  the  fraction  is  the  cut  or  fill  at  a 
distance-out  (offset)  indicated  by  the  denominator. 


70 


ROAD  LOCATION 
CROSS-SECTION   NOTES 


Sta. 

B.S. 

F.S. 

H.I. 

ELEVATION 

Cut 
or 
Fill. 

Ground 

Grade 

327 
328 
329 

105.3 
94.6 

98.4 

95.2 
99.2 

8.9 

8.0 

8.0 

-4.6 

3.2 
-4.6 

0 

7 

-4.0 

-9.0 

20.8 

23.5 

19.9 

16.0 

(a)  (6) 

Level  Section  Three  Level  Section  Five  Level  Sectfc* 

FIG.  35. — Cross-sections. 

CALCULATING  QUANTITIES 

Each  portion  of  the  roadway  between  stations  may  be  con- 
sidered to  be  a  prismoid  and  the  areas  of  the  ends  may  be 
determined  and  the  prismoidal  formula  applied.  But  this 
refinement  will  not  usually  be  necessary.  The  calculations  are 
simpler  for  the  approximate  method,  of  averaging  end  areas 
and  when  bids  are  based  upon  it,  they  will  be  reasonably  close 
and  fair.  If  A\  and  A  2  are  the  end  areas,  and  I  the  length,  the 
volume 


Stated  in  words. 

To  get  the  volume:  Multiply  the  half -sum  of  the  end  areas  by 
the  axial  length  of  the  prismoid. 

If  areas  are  in  square  feet  and  length  in  feet,  the  volume  will 
be  in  cubic  feet;  it  may  be  reduced  to  cubic  yards  by  dividing 
by  27.  To  apply  this  rule  the  end  areas  will  have  to  be  calcu- 
lated. 


CROSS-SECTION  AREAS  71 

End  Areas. — When  the  center  and  side  heights  of  a  cross- 
sectional  area  are  the  same  it  is  a  one-level  section;  when  the 
center  and  side  heights  differ  it  is  a  three-level  section;  when 
the  height  is  found  at  five  places  it  is  a  five-level  section,  and 
so  on.  (See  Fig.  35.) 

In  any  case  the  section  may  be  divided  into  triangles  and 
trapezoids  and  the  areas  found.  The  following  rules  may  be 
easily  verified  by  geometry. 

Area  of  a  three-level  section:  Multiply  the  half -sum  of  the 
side  heights  by  the  half-base  and  to  this  add  the  product  of  the 
center  height  by  the  half-sum  of  the  distances-out. 


EXERCISES 

1.  Express  this  rule  for  a  one-level  section. 

2.  Verify  the  rule  by  dividing  the  section  into  four  triangles  as  indi- 
cated in  Fig.  35  (6). 

3.  Verify  the  rule  by  considering  the  section  made  up  of  two  trapezoids 
minus  two  end  triangles. 

For  a  section  having  more  than  three  levels,  the  method  can 
0 


.be  best  illustrated  by  a  diagram.     The  notes  are  written  in  the 
fractional  form  with  the  addition  of  7  at  each  end,  and  0  under 

the  central  ho.  Beginning  at  the  center,  multiply  heights  by 
distances-out  in  pairs  as  indicated  by  the  sloping  lines.  Call 
those  products  connected  by  the  full  lines  positive,  those  con- 
nected by  the  dotted  lines  negative.  All  distances-out  are  posi- 
tive, heights  are  positive  for  cuts  and  negative  for  fills.  The 
area  then  is 


4  — 

^1  


h0di+hid2+h2b       1       f     Qhi+dih2+d20      1 


(1) 


Applying  this  to  Fig.  35  (c),  consider  the  figure  made  up  of 
four  trapezoids  less  two  end  triangles. 


72 


ROAD   LOCATION 


Area  of  trapezoid  EFGK  =  $(hi+h2)(d2-di). 

Area  of  trapezoid  CEKL  =  %(ho+hi)di. 

Area  of  triangle  F  JG    •     =  Jfo  (cfc  -  &)  . 

Hence  the  area  of  the  section  on  the  right  of  the  center  line 

l  -h2(d2  -b)} 


The  area  on  the  right  may  be  found  in  exactly  the  same  manner. 
Added  together,  the  result  is  the  same  as  found  above  (1). 
Mr.  E.  U.  Bryan,  Modesto,  Cal.,  applies  an  old  rule  thus:  1 


FIG.  36. 

Stated  in  words:  "  Begin  at  any  point  on  the  section  and 
proceed  in  either  direction  (clockwise  or  counter-clockwise), 
multiplying  each  cut  (or  fill)  in  its  order  by  the  horizontal  dis- 
tance between  the  point  just  preceding  and  the  point  just  suc- 
ceeding. In  cases  where  one  passes  to  the  right  in  measuring 
the  horizontal  distance  from  the  preceding  to  the  succeeding 
point  the  product  obtained  by  multiplying  this  distance  by  the 
cut  (or  fill)  at  intermediate  point  is  of  one  sign  and  in  cases 


Eng.  Record,  p.  470,  Oct.  24,  1914. 


MISCELLANEOUS  73 

where  one  passes  to  the  left  the  product  is  of  the  opposite  sign. 
Take  one-half  of  the  difference  between  the  sums  of  products 
of  opposite  signs  and  the  result  is  the  area  of  the  section." 

EXERCISES 

1.  Find  the  area  of  the  cross-section  station  327.  level  notes,  p.  70 
for  a  20-foot  roadway  in  fill  and  24  feet  in  cut.  Ans.  111.5  sq.  ft. 

2.  Find  the  area  of  the  cross-section  station  329  same  page. 

NOTE:  Part  of  section  327  is  in  fill  and  part  in  cut.  As  it  is  usual  to 
pay  for  either  cuts  or  fills  and  not  for  both  it  is  customary  to  compute 
each  part  separately  and  record  in  columns  set  apart  for  ''cut"  and  "fill" 
in  the  quantity  book.  The  same  rules  will  apply  by  considering  the  sec- 
tion as  two  sections  with  readings  thus: 

?-i    ®iP-  ?_2    <L? 

20.8     8.0  7.0 

0.0     OJ)      -9.0  Ans.  Cut    125.0  square  feet. 

7TO      2375  Fill     13. 5  square  feet. 

As  a  check  on  the  work  each  cross-section  may  be,  and  by  some  engi- 
neers is  always,  plotted  on  squared  paper,  and  the  area  obtained  by  a 
planimeter  or  the  number  of  squares  counted. 


MISCELLANEOUS 

Crown. — In  road  work  where  the  quantities  have  been 
determined  by  the  foregoing  methods  there  must  be  added  to 
the  quantities  in  fills  and  subtracted  from  those  in  cuts  the 
amount  necessary  for  the  crown.  With  plane  surfaces  the  end 
section  is  a  triangle  with  area,  Jfrc,  where  b  is  the  base  width  of 
the  crown  and  c  the  mid-height.  With  the  parabolic  form  of 
crown  the  end  area  is  ^  be.  The  quantities  given  in  Table  V, 
p.  50,  which  is  for  plane  surface,  must  be  multiplied  by  f  to  get 
the  corresponding  quantities  for  a  parabolic  surface. 

Blade  Grader  Work. — Where  the  excavations  and  embank- 
ments are  not  large  and  the  grading  can  be  done  with  a  blade 
grader,  it  is  often  better  to  pay  for  the  work  on  a  time  basis,  or 
some  other  method  of  compensation,  thus  saving  the  expense 
of  earth  computation. 


74  ROAD  LOCATION 

Shrinkage. — Earth  taken  from  a  hole  and  piled  loosely 
will  occupy  more  space  than  when  in  its  original  position, 
varying  from  10  to  20  per  cent  for  earth,  and  from  50  to  70 
per  cent  for  solid  rock.  But  when  the  earth  is  placed  in  an 
embankment  or  tamped  into  a  ditch  it  will  occupy  less  space. 
The  amount  of  shrinkage  depends  upon  the  character  of  the 
earth,  on  the  method  of  depositing,  upon  its  state  of  moisture, 
and  upon  the  height  of  embankment.  Loamy  and  light  sandy 
earth  will  shrink  about  12  per  cent;  clay  arid  clayey  earth, 
10  per  cent;  gravel,  8  per  cent;  while  solid  rock  will  expand 
from  50  to  70  per  cent.  As  to  the  method  of  depositing  the 
shrinkage  from  pit  measurements  is  probably  greatest  when  the 
embankment  is  made  by  drag  scrapers  where  the  horses  and 
drivers  are  continually  walking  over  the  deposited  earth.  Earth 
spread  in  shallow  layers  and  compacted  by  thorough  harrowing 
and  rolling  may  come  next.  Then,  perhaps,  without  rolling, 
wheel  scrapers,  wagons,  cars,  and  wheelbarrows.  Damp  earth 
will  compact  better  than  dry  earth,  embankments  laid  up  during 
rainy  weather  show  more  shrinkage  from  pit  measurements  and 
less  settlement  than  those  laid  in  dry  weather.  The  higher  the 
embankment  the  greater  the  weight  on,  and  consequently 
the  compaction  of  the  lower  layers. 

Settlement. — The  shrinkage  mentioned  in  the  preceding 
paragraph  takes  place  during  construction.  In  time  the 
embankment  will  shrink  further  due  to  settlement,  a  slow 
rearrangement  of  the  particles  composing  it  into  more  stable 
positions  under  the  weight  of  the  super  load  and  jarring  of 
vehicles.  The  greater  the  shrinkage  during  construction  the 
less  will  be  the  settlement.  Consequently  the  settlement  of 
earth  will  be  in  inverse  order  of  that  given  above  for  the  shrink- 
age from  pit  measurements;  likewise,  the  percentage  of  set- 
tlement of  low  embankments  will  be  greater  than  that  of  high. 

To  compensate  for  settlement  it  is  customary  to  set  the 
grade  stakes  (on  low  grades  only  the  finishing  stakes)  about  10 
per  cent  higher  than  the  calculated  values,  for  example,  instead 
of  setting  the  finishing  stake  for  a  fill  of  2.1  it  is  set  for  a  fill  of 
2.3.  Iowa  Highway  specifications  for  depth  of  fill  up  to  5  feet 


EXISTING  ROAD  LAYOUTS  75 

allow  15  per  cent;  from  5  to  12  feet,  12  per  cent;  from  12  to  18 
feet,  10  per  cent.  With  rock  it  is  not  customary  to  allow  for 
settlement,  but  the  amount  will  depend  upon  the  size  and  shape 
of  the  stones  used,  varying  from  nothing  for  large  angular 
stones  to  8  per  cent  for  gravel. 

Borrow  Pits. — Where  the  cuts  and  fills  do  not  balance,  or 
where  the  haul  is  long,  it  is  advantageous  to  "  borrow  "  earth 
from  excavations  alongside  the  road.  Borrow  pits  should  be 
regular  in  form,  so  they  can  be  measured  easily.  They  should 
always  be  a  little  distance  from  the  toe  of  the  slope,  leaving  a 
berm  increasing  from  6  feet,  say,  with  height  of  embankment. 

Wasted  Earth. — Sometimes  earth  from  cuts  must  be 
'wasted.  This  can  be  done  frequently  by  widening  the  em- 
bankment at  the  foot  of  the  cut.  Otherwise  it  may  be  neces- 
sary to  secure  permission  to  place  it  on  adjacent  land. 

EXISTING  ROAD  LAYOUTS 

The  matter  of  surveying  has  been  gone  into  with  consider- 
able detail.  Such  refinement  will  seldom  be  necessary.  For 
example,  the  preliminary  survey  and  the  final  location  can  be 
combined  into  a  single  operation  and  done  by  two  men.  Even 
the  leveling,  if  not  omitted,  can  be  run  by  the  transit  and  the 
curves  and  grades  staked  in  by  eye.  But  as  populations 
become  denser  and  traffic  increases  more  money  will  be  spent 
in  higher-priced  roads,  there  will  be  a  demand  for  straighter 
roads  with  easier  grades.  Calf-path  trails  and  section-line 
roads  will  have  to  give  way  for  scientifically  located  and  con- 
structed highways. 

Relocations  along  Existing  Lines. — Where  the  relocation 
is  not  along  existing  lines  it  becomes  a  new  location  and  some 
of  the  methods  given,  or  some  modification  of  them  may  be 
applied.  However,  when  the  road  is  to  be  relocated  approx- 
imately along  existing  lines  the  surveyor  can  do  little  but 
eliminate  short  crooks  and  bends,  smooth  out  and  better  the 
grades  by  cuts  and  fills,  and  perfect  the  drainage  by  proper  use 
of  ditches,  tiling,  culverts,  and  bridges.  Where  possible  the 


76  ROAD   LOCATION 

true  location  of  the  right  of  way  should  be  determined  by 
finding  government  corners,  if  these  still  exist,  or  others  estab- 
lished by  reliable  authority  if  this  can  be  done  without  expend- 
ing too  much  time.  Some  State  highway  departments  locate 
and  tie  out  these  marks  if  easily  obtainable ;  if  not,  they  assume 
the  proper  location  of  the  highway  to  be  outlined  by  long- 
established  fence  rows.  The  right  of  way  having  been  deter- 
mined or  assumed  the  relocation  is  made  within  these  limits  as 
far  as  practicable.  Occasionally  to  avoid  a  swamp,  bad  angle, 
steep  hill,  or  other  feature  there  must  be  new  locations  for  short 
distances. 

A  party  for  relocation  work  may  consist  of  as  few  as  three 
men;  an  instrument  man,  who  is  also  chief  of  party;  and  two 
assistants  who  act  as  chainmen,  rodmen,  axmen,  and  so  forth, 
as  occasion  may  require.  They  will  ordinarily  have  an  auto- 
mobile or  other  conveyance  to  take  them  to  and  from  the  work 
and  to  haul  instruments,  stakes,  and  other  supplies.  The 
outfit  required  will  be  one  combined  transit  and  level,  one  level- 
ing rod,  two  flag  poles,  one  set  of  11  steel  marking  pins,  one  100- 
foot  steel  tape,  one  50-foot  metallic  tape,  one  ax,  a  supply  of 
stakes,  nails  of  various  sizes,  tacks,  red  cloth  for  patches,  and 
note  books  and  pencils.  If  the  country  is  rough  a  level  board 
for  cross-sectioning  will  be  found  handy.  A  corn  knife  for  cut- 
ting corn  stalks  and  high  weeds  will  be  convenient  at  times.  If 
the  party  is  to  establish  grade  lines  profile  and  drafting  paper 
and  instruments  will  be  required.  A  small  chest  or  trunk  in 
which  to  keep  such  articles  as  tapes,  note  books,  pencils,  draw- 
ing instruments,  and  other  supplies  safe  from  rain  storms  or 
marauding  hands  is  highly  desirable. 

Surveying  Operations. — A  traverse  line  is  run  near  the 
center  of  the  right  of  way.  Twenty-penny  wire  nails  driven 
through  a  patch  of  red  cloth  flush  with  the  ground  will  serve  to 
mark  the  stations.  Ordinarily  these  will  not  be  disturbed  by 
the  traffic.  Hubs  should  be  set  flush  with  the  ground  and  tied 
out  in  the  ordinary  manner.  After  a  short  line  of  traverse  has 
been  surveyed  the  same  party  can  run  levels  over  it  and  get 
cross-sections  at  each  station  and  sudden  break  in  ground. 


FIELD  AND  OFFICE   OPERATIONS  7.7 

The  notes  will  usually  be  sent  to  headquarters  for  plotting  and 
computations;  but  in  some  cases  the  party  may  do  this  work, 
establish  a  grade  line  and  set  grade  stakes. 

Office  Work. — After  the  grade  stakes  have  been  set  the 
cross-sections  are  plotted,  end  areas  measured  by  a  planimeter  or 
computed  by  methods  heretofore  given.  Cross-sections  should 
be  plotted  on  cross-section  (squared)  paper  so  that  by  counting 
the  squares  there  may  be  a  rough  check  on  the  planimeter  com- 
putation. Or,  an  accurate  measure  of  the  cross-section  may  be 
made  by  adding  together  the  average  height  of  each  foot  space 
across  the  section,  the  sum  being  the  area  in  square  feet.  As 
these  sections  are  small  and  irregular  the  use  of  the  planimeter 
is  the  only  practical  method  of  obtaining  the  areas  with  speed 
and  accuracy.  The  planimeter  should  be  run  around  the  area 


^Drilled  Hole 


FIG.  37. — Template  for  Plotting  the  Crown  of  a  Road 

twice,  the  readings  noted  at  the  end  of  each  run,  the  second 
reading  should  be  twice  the  first.  Harger  and  Bonney  l  state 
that  a  satisfactory  rule  is  to  allow  a  difference  of  0.4  square  foot 
for  areas  up  to  50  square  feet  and  1.0  square  foot  error  above 
50  square  feet.  Also  that  it  is  best  to  have  two  men  work 
independently  with  separate  planimeters  and  check  the  one 
against  the  other.  To  assist  in  plotting,  standard  templates  of 
the  crown  of  the  roadway  for  cuts,  low  fills  and  high  fills  may 
be  made  from  transparent  celluloid,  Fig.  37.  Broken  triangles 
can  be  thus  utilized. 

Field  Procedure. — During  the  process  of  construction  the 
survey  party  will  keep  the  road  surveyed  and  staked  ahead 
of  the  graders,  from  time  to  time  check  the  work  of  the  con- 

1  " Highway  Engineers'  Handbook,"  by  Harger  and  Bonney,  McGraw- 
Hill  Book  Co.,  New  York, 


78  ROAD  LOCATION 

struction  gang,  stake  out  culvert  and  bridge  openings,  as  may  be 
required,  measure  borrow  pits,  make  estimates  on  the  amount 
of  work  done,  at  the  end  of  each  month,  set  finishing  grade 
stakes  in  the  center  of  the  graded  way  just  before  its  completion, 
and  do  such  other  work  as  may  be  required  by  those  in  authority 
even,  perhaps,  to  the  acceptance  of  the  finished  work. 

Stadia  Surveying. — Stadia  surveys  for  maps  or  traverses 
may  be  made  with  either  transit,  or  plane  table  equipped  with 
telescopic  alidade.  The  Plane  Table,  since  details  and  natural 
features  are  sketched  in  the  field,  furnishes  a  convenient  in- 
strument for  preliminary  work.  By  means  of  a  stadia-rod 
distances  to  any  desired  point  may  be  quickly  found  and  the 
elevation  of  the  point  calculated  trigonometrically  or  with  re- 
duction tables.  The  Beaman  Stadia  Arc  is  advantageous  for 
finding  these  elevations.  If  contour  lines  are  desired  the  plane 
table  may  be  set  so  that  H.  I.  is  approximately  on  a  contour, 
or  at  a  known  distance  above  or  below,  and  as  many  points 
as  needed  shot  in  and  sketched  on  the  map.  By  resetting  the 
table  as  many  contours  as  wanted  may  be  determined.  In 
running  traverses  the  table  is  oriented  by  back-sighting  on  the 
previous  table  station  and  another  station  ahead  located  by 
stadia  shot.  Side  shots  to  points  visible  from  more  than  one 
station  will  furnish  convenient  checks  upon  the  work.1 

1  For  fuller  details  of  stadia  methods  see  standard  works  on  survey- 
ing, such  as,  Breed  and  Hosmer's  "  Surveying,"  Vols.  I.  and  II.,  Wiley 
&  Sons,  New  York;  also  "A  Treatise  on  the  Plane  Table,"  by  D.  B. 
Wainwright,  U.  S.  Coast  Survey  Report,  1905. 


CHAPTER  III 
TYPES  AND  ADAPTATION  OF  ROADS 

To  secure  the  kind  of  road  best  adapted  to  any  particular 
place  is  not  an  easy  task.  While  economic  and  other  engineering 
principles  should  be  involved,  the  real  determining  factor  will 
usually  be  some  local  consideration.  The  wishes  and  opinions 
of  the  people  who  live  along,  use  and  pay  for  any  road  improve- 
ment, even  though  they  have  never  studied  the  scientific  prin- 
ciples of  transportation  and  road  making,  should  have  much 
weight.  The  final  test  of  success  will  be  the  satisfaction  of 
these  people.  The  tactful  engineer  will  present  facts  and 
strongly  advocate  good  materials  and  good  construction,  well 
suited  to  the  conditions,  but  will  nevertheless  bend  to  constrain- 
ing influences  and  do  the  very  best  he  can  with  the  means  and 
materials  at  hand. 

The  main  points  to  be  considered  in  the  selection  of  a  type  of 
road  are: 

1.  The  amount  and  character  of  the  traffic. 

2.  The  character  of  the  location  as  to  drainage,  grades,  and 

soil. 

3.  Climatic  and  weather  conditions. 

4.  Available  building  materials. 

5.  First  cost  and  annual  charges. 

6.  Cost  of  maintenance. 

7.  Durability. 

8.  Smoothness,  hardness,  tractive  resistance. 

9.  Slipperiness — animals,  pedestrians,  motors. 

10.  Sanitariness — healthfulness,  noisiness,  mud,  dust. 

11.  Acceptability — esthetics,   heat,   light,   comfort,   desires 

of  the  users. 

79 


80  TYPES  AND  ADAPTATION  OF   ROADS 

While  these  items  may  be  considered  individually  with 
respect  to  any  particular  road,  they  must  also  be  considered 
collectively.  Likewise  they  are  not  absolutely  independent  of 
each  other.  Durability  is  a  function  of  climate,  character  and 
amount  of  traffic,  hardness  and  smoothness,  drainage,  cleanli- 
ness, and  possibly  other  items.  Smoothness  and  hardness 
increases  slipperiness.  Cost  depends  upon  availability  of 
materials,  and  so  on. 

TYPES  OF  ROADS 

Earth  Road. — By  far  the  most  common  is  the  ordinary  earth 
road.  Of  the  more  than  two  and  a  quarter  million  miles  of 
roads  in  the  United  States,  about  90  per  cent  are  earth  roads, 
and  many  have  not  even  been  graded.  This  indicates  the 
importance  of  the  earth  road,  and  while  the  surfacing  of  roads 
will  continue  indefinitely,  it  is  not  expected  or  desirable  that  a 
very  large  percentage  of  the  earth  roads  ever  will  be  surfaced 
with  harder  materials.  In  many  of  our  Prairie  States  every 
section  line  is  made  by  law  a  road.  Suppose  the  north  and 
south  and  the  east  and  west  roads  meeting  at  the  center  of  each 
township  were  surfaced.  While  this  would  be  as  unscientific 
as  the  laying  out  of  these  roads  was,  every  farmer  would  be 
within  three  miles  of  a  surfaced  road  and  only  16f  per  cent  of 
all  roads  would  be  surfaced.  If  10  per  cent  of  the  roads  were 
surfaced  and  these  selected  with  judgment  they  would  amply 
accommodate  90  per  cent  of  the  traffic. 

The  earth  road  when  it  can  be  graded  with  the  blade  road 
grader  and  a  traction  engine  can  be  very  cheaply  constructed, 
costing  from  $35  to  $100  per  mile,  exclusive  of  culverts  and 
bridges.  These  perhaps  double  the  cost.  The  road  can  be 
maintained  by  the  road  drag  at  a  cost  of  $10  to  $25  per  mile  per 
year.  The  annual  cost  of  maintaining  bridges  and  culverts  will 
depend  upon  the  character  of  those  structures  as  well  as  the 
weather  conditions,  floods  and  soil,  assuming  this  to  amount 
to  as  much  as  dragging,  there  results : 

First  cost  of  earth  roads  including  culverts. .  .   $70  to  $200 

Maintenance  of  earth  roads  including  culverts  20  to      50 


EARTH   ROADS  81 

The  good  qualities  of  an  earth  road  are: 

Low  first  cost. 

Not  slippery. 

Noiseless. 

Easy  on  horses'  feet. 

Comfortable  when  in  first-class  condition. 
The  poor  qualities  are: 

High  tractive  resistance. 

Not  durable.     High  cost  of  maintenance  needing  con- 
stant attention. 

Difficult,  practically  impossible  to  clean. 

Muddy  in  wet  weather. 

When  the  dust  blows  away  is  left  choppy. 

Ruts  easily. 

Wears  down  rapidly  under  heavy  traffic  in  windy  locali- 
ties. 

Uncomfortable  except  when  in  prime  condition. 
The  road  is  satisfactory  if  well  drained  and  maintained, 
under  light  or  moderate  traffic.     As  soon  as  the  traffic  becomes 
heavy,  ruts  and  pockets  form  and  it  is  practically  impossible 
to  keep  it  in  good  condition  or  repair. 

The  character  of  the  soil  has  much  to  do  with  the  condi- 
tion of  the  road  surface.  Clay  soils  become  soft  and  sticky  in 
wet  weather  and  hard  and  choppy  in  dry  weather.  Gumbo 
soils  are  very  sticky  in  wet  weather  and  rut  badly.  They  dry  up 
rough  and  are  a  long  while  wearing  smooth.  Sandy  soils  are 
best  in  wet  weather,  as  sand  itself  has  no  cementing  power, 
depending  on  the  water  for  that  property.  When  dry,  there- 
fore, sand  roads  are  in  their  poorest  condition.  Some  soils, 
like  field  soils,  are  a  sandy  loam;  such  soil  makes  good  earth 
roads  for  all  kinds  of  weather. 

Sand-clay  Roads. — Sand  being  best  in  wet  weather  and 
poorest  in  dry,  while  clay  is  the  opposite,  a  right  proportion  of 
the  two  makes  a  fairly  good  road  surface.  This  type  is  very 
appropriate  for  roads  having  a  light  or  moderate  traffic  over 
sandy  stretches  or  over  clay  and  gumbo  soils.  The  cost  will 
depend  upon  the  availability  of  materials.  Roads  actually 


82  TYPES  AND  ADAPTATION  OF  ROADS 

constructed  range  in  price  from  $500  to  $1500  per  mile.  Main- 
tenance cost  will  be  about  the  same  as  for  earth  roads. 

Gravel  Roads. — Where  gravel  of  good  quality  can  be  readily 
obtained,  this  may  be  spread  over  the  road  surface  and  when 
compacted  by  the  traffic  forms  a  smooth,  non-slippery,  non- 
muddy,  noiseless,  comfortable,  driveway.  Gravel  roads  get 
dusty  and  rutted  in  dry  weather,  especially  under  heavy  traffic. 
They  are  to  be  commended  for  park  drives,  house  drives  or 
rural  roads  where  there  is  a  moderate  amount  of  traffic. 

Macadam  Roads. — These  are  roads  made  of  broken  stone 
thoroughly  compacted  by  roller  or  traffic.  They  are  cemented 
by  fine  particles  of  stone  or  clay  and  when  in  good  condition  form 
an  excellent  road  for  horse  and  iron-tired  vehicle  traffic.  The 
horses'  shoes  and  the  iron  tires  wear  away  enough  dust  from  the 
stone  to  keep  the  top  surface  thoroughly  cemented.  With 
tough  stone  and  not  too  heavy  a  traffic,  they  remain  smooth 
and  hard  under  such  conditions,  and  never  become  slippery. 
Motor  traffic,  however,  due  to  the  shearing  effect  of  the  drive 
wheels,  has  a  tendency  to  loosen  the  stones  and  start  raveling. 
Most  of  the  famous  good  roads  of  Europe  are  of  this  type. 
Until  the  advent  of  the  automobile,  they  were  thought  to  be 
almost  ideal  for  rural  roads. 

Bituminous  Macadam  Roads. — Because  "  waterbound  mac- 
adam "  roads  deteriorated  under  the  action  of  automobile 
traffic,  as  has  been  stated  on  account  of  the  shearing  effect  of 
the  drive  wheels  and  also  because  the  rubber  tires  failed  to 
furnish  the  stone  dust  to  re-cement  continually  the  road  sur- 
face, experiments  were  made  in  cementing  the  stone  pieces 
with  tar  and  asphalt-bitumens.  These  roads  have  proven 
quite  popular  for  all  except  extremely  heavy  traffic.  They  are 
smooth,  easy  riding,  of  small  tractive  resistance  and  comfortable. 
They  must  be  placed  upon  a  concrete  or  macadam  foundation, 
as  the  bituminous  material  is  plastic  and  the  surface  will  con- 
form to  any  depression  in  the  subgrade  below.  The  concrete 
foundation  furnishes  the  required  stiffness.  For  roads  with 
moderately  heavy  traffic  leading  into  the  larger  cities  they  are 
well  adapted. 


VARIOUS  ROAD  TYPES  83 

Brick  Roads. — Vitrified  paving  brick  make  a  hard  and  dur- 
able surface  having  a  low  tractive  resistance;  the  surface  is 
reasonably  smooth  and  non-slippery.  It  is  noisy,  although  the 
noise  is  somewhat  reduced  by  filling  the  joints  with  bituminous 
filler.  It  is  sanitary  and  can  be  cleaned  by  flushing  or  sweeping. 
It  is  well  adapted  to  places  where  there  is  heavy  traffic  either 
with  teams,  tractors  or  motor  trucks.  Brick  has  been  found  to 
be  thoroughly  serviceable  for  country  roads  leading  into  large 
cities.  The  first  cost  is  considerable,  but  annual  maintenance 
is  not  great.  Just  what  the  life  of  such  roads  may  be  is  not 
known;  roads  thirty  years  old  are  still  in  good  condition.  So 
much  depends  upon  the  quality  of  the  brick — no  two  clays  giving 
exactly  the  same  results,  upon  the  manner  of  laying,  upon  the 
character  of  the  foundation,  and  upon  climatic  conditions,  that  it 
is  not  safe  to  make  specific  statements  regarding  durability. 

Concrete  Roads. — This  type  of  road  is  comparatively  new 
and  it  can  hardly  be  asserted  that  it  is  more  or  less  durable 
than  other  roads.  Concrete  roads  seem  to  be  well  adapted  for 
automobile  traffic;  under  such  traffic  they  remain  smooth, 
have  easy  traction  and  are  not  slippery.  Under  heavy  teaming 
with  iron  wheels  it  is  doubtful  if  they  would  prove  as  durable 
as  some  other  types.  The  cost  is  a  little  less  than  brick,  and 
when  made  in  two  or  three  courses,  about  the  same  as  bitumi- 
nous macadam. 

Asphalt  Blocks. — Blocks  about  5  inches  wide,  12  inches  long 
and  2  inches  deep  are  manufactured  of  crushed  rock  and  asphalt 
in  a  central  plant  under  uniformity  of  mixture  and  pressure. 
These  are  laid  on  a  concrete  or  macadam  base  as  bricks  and 
soon  cement  together  under  traffic  into  a  smooth  surface  looking 
much  like  asphaltic  macadam  or  sheet  asphalt.  They  have 
been  successfully  used  for  country  roads  under  a  variety  of 
traffic.  Being  in  the  form  of  blocks  special  equipment  for 
laying  is  not  necessary.  The  first  cost  is  about  the  same  as  a 
brick  road. 

Sheet  Asphalt. — This  type  of  road  while  very  popular  for 
street  paving  has  not  yet  been  used  greatly  for  rural  roads. 
It  is  at  its  best  where  it  receives  a  moderate  traffic  sufficient  to 


84  TYPES  AND  ADAPTATION  OF  ROADS 

keep  it  packed  hard.  The  asphalt  and  sand  surface  has  a 
property  of  swelling  and  cracking  if  not  used.  It  therefore 
should  never  be  put  where  any  part  of  it  will  lie  idle  a  great 
share  of  the  time. 

Wheelways. — Stone,  concrete,  and  steel  have  been  utilized 
to  form  parallel  tracks  upon  which  the  wheels  of  vehicles  travel, 
the  center  being  filled  with  various  other  materials.  Telford 
built  a  road  having  wheelways  of  stone:  "  The  blocks  were  of 
granite,  12  inches  deep,  14  inches  wide,  and  not  less  than  4  feet 
long."  He  used  under  this  a  telford-gravel  foundation,  and 
between  the  wheelways  broken  stone. 

A  number  of  forms  of  steel  wheelways  have  been  proposed 
and  in  some  instances  successfully  used.  From  Valencia  to 
Gras,  Spain,  is  a  noted  steel  wheelway  over  which  many  tons  of 
freight  are  annually  hauled.  The  traffic  is  said  to  be  over  3000 
vehicles  daily.  This  is  a  particular  case,  adapted  to  particular 
conditions  and  cannot  be  followed  generally. 

A  few  years  ago  General  Dodge,  formerly  Director  of  the 
U.  S.  Office  of  Public  Roads,  used  his  influence  to  popularize 
steel  trackways.  And  while  it  is  conceded  that  they  have  some 
advantages  they  have  not  been  even  moderately  adopted  by  road 
builders.  In  a  place  like  that  in  Spain,  where  there  is  an 
extremely  heavy  freight  traffic  for  a  short  distance,  no  doubt 
they  would  prove  economical. 

Burned  Clay  Roads. — For  many  years  the  railroads  have 
burned  clay  and  gumbo  for  ballast.  A  trench  is  dug  in  the  clay 
soil,  in  the  bottom  wood  is  piled,  over  this  coal,  over  this  is 
thrown  a  layer  of  clay,  then  other  layers  of  coal  and  clay  are 
piled  on  this,  each  a  little  nearer  the  bank  from  which  the  clay 
is  thrown.  Thus  as  the  fire  burns  the  pile  is  moved  sidewise  a 
little.  The  clay  burns  into  angular,  reddish  lumps  about  as 
hard  as  ordinary  brick.  The  material  is  too  porous  for  a  good 
road,  but  on  account  of  its  reddish  color  is  a  valuable  covering 
for  ground  in  parks  which  traffic  occasionally  passes  and  in 
contrast  with  gray  stone  drives  and  paths  may  be  formed  into 
pleasing  figures. 

Shell  Roads. — Along  the  Atlantic  and  Gulf  of  Mexico  sea- 


VARIOUS  ROAD  TYPES  85 

boards  oyster  shells  being  abundant  have  been  utilized  in 
road  making.  For  light  driving  they  make  a  fairly  acceptable 
roadway.  The  shells  are  not  sufficiently  tough  to  withstand 
heavy  traffic,  hence  soon  become  ground  into  powder,  forming 
dust  and  mud. 

Furnace  Slag  has  been  used  to  a  limited  extent  for  roads. 
It  lacks  toughness  but  is  applicable  for  light  traffic. 

Coal  Slack. — Near  coal  mines  waste  coal  slack  has  been 
used  on  the  roadways.'  It  does  not.  make  as  good  a  road  as 
gravel. 

Cinders. — Cinders  are  frequently  used  for  park  drives  where 
heavy  teaming,  of  course,  is  not  allowed,  being  porous,  the  rain 
soon  sinks  away,  leaving  no  mud.  Cinder  roads  are  better 
than  earth  roads  and  can  be  utilized  advantageously  in  the 
several  drives  about  the  farmstead. 

Plank  Roads. — Years  ago  plank  roads  were  common  and* 
even  yet  in  the  lumbering  regions  of  the  Northwest,  where  rain 
is  plentiful  and  plank  cheap,  roads  of  this  sort  are  still  con- 
structed. Two  stringers  are  laid  lengthwise  upon  which  are 
spiked  crosswise  the  planks  about  8  feet  long.  The  writer  has 
read  in  an  old  paper  an  article  asking  the  town  council  not  to 
allow  railroads  to  enter  Chicago  because  they  would  destroy 
the  plank-road  industry. 

Corduroy  Roads. — Small  logs  or  poles  are  laid  down  across 
the  roadway.  They  are  makeshifts  used  to  cross  muddy 
places  in  timbered  country.  They  were  quite  common  during 
the  Civil  War  to  transport  army  supplies  to  unsettled  loca- 
tions. 

Hay  Roads. — Just  before  the  rainy  season  in  the  Northwest 
hay  or  straw  is  often  strewn  upon  the  roads.  This  prevents 
them  from  becoming  muddy  during  the  long  wet  season.  The 
straw  is  only  a  temporary  palliative,  just  as  brush  is  sometimes, 
used  in  a  timbered  country,  crushed  sugar  cane  in  the  South, 
and  other  waste  products  everywhere. 

Strawing  roads  in  the  sand  hills  of  western  Nebraska  and 
neighboring  States  may  be  considered  something  more  than 
temporary  improvement.  The  straw  is  spread  upon  the  sand 


86 


TYPES  AND  ADAPTATION  OF  ROADS 


with  a  manure  spreader.  It  mixes  with  the  sand,  decays  and 
after  a  series  of  years  a  loam  is  formed,  and  the  road  becomes 
similar  to  any  other  earth  road. 


COMPARISON  OF  ROADS 

A  comparison  of  several  roads  for  a  particular  place  can  be 
made  by  the  forming  of  a  table  in  which  the  essentials  are 
written  along  the  left-hand  side  with  their  weighted  values 
and  the  roads  to  be  compared  along  the  top,  thus: 


DO    « 

1 

"^  ~i 

H 

T3 

- 

o 

•2J 

J 

0 

0 

H 

^ 

0 

ia 

•5 

* 

1 

'i 

« 

o 

3 

o 

1 

• 

•81 

1 

§ 

""55 

. 

f§ 

1 

|s 

11 

I 

O 

1 

1 

c 

a 

! 

t/2  *^ 

o  o 
£  o 

Low  first  cost  

20 

20 

16 

16 

15 

10 

12 

10 

8 

14 

Low   cost   of    mainte- 

nance 

20 

15 

15 

10 

8 

9 

8 

8 

10 

g 

Ease  of  traction  

10 

1 

4 

6 

8 

10 

10 

9 

9 

9 

Non-slipperiness 

10 

9 

9 

9 

9 

8 

5 

5 

5 

5 

Noiselessness  

5 

5 

5 

5 

4 

1 

1 

2 

4 

2 

Healthfulness  

10 

5 

5 

6 

8 

9 

9 

9 

8 

9 

Freedom  from  dust  and 

x 

mud  

10 

1 

2 

3 

4 

9 

9 

9 

9 

9 

Comfortable  to  use.  .  .  . 

10 

3 

4 

5 

6 

8 

8 

9 

9 

9 

\    Appearance 

5 

2 

3 

3 

4 

5 

4 

5 

(- 

5 

Total  ;  

100 

61 

63 

63 

66 

69 

.66 

66 

67 

70 

It  must  be  remembered  that  a  table  such  as  this  applies 
only  to  an  individual  road.  No  two  will  be  exactly  alike.  First 
.cost  may  be  a  large  determining  factor;  it  may  be  ranked  at 
50  or  more,  while  healthfulness  might  be  0.  Local  conditions, 
as  has  been  frequently  stated,  are  always  to  be  taken  into 
account. 


CHAPTER  IV 
DRAINAGE 

DRAINAGE  is,  perhaps,  the  most  important  element  connected 
with  road  making.  If  the  road  be  of  sand  the  drainage  should 
be  such  as  to  keep  it  continually  moist,  if  of  clay,  continually 
dry.  Extreme  drying  out  is  bad  for  a  waterbound  macadam, 
but  a  wet  foundation  is  worse.  Roads  upon  level,  ridges  and 
valleys  are  harder  to  maintain  in  good  condition  than  those  on 
slightly  rolling  land,  primarily  because  of  bad  drainage.  The 
effect  of  the  water  is  the  same  whether  it  soaks  in  from  the  top 
or  seeps  up  from  the  bottom.  Therefore,  drainage  must  look 
after  the  water  from  both  directions.  Usually,  therefore,  the 
subject  is  discussed  under  the  two  heads  of  surface  drainage  and 
sub-drainage.  Drainage,  also,  has  to  do  with  the  taking  care 
of  all  surplus  water  that  may  come  near  the  roadway;  bridges 
and  culverts  might  very  properly  be  a  sub-heading  of  this  sub- 
ject. 

SURFACE  DRAINAGE 

On  all  roads  the  surface  is  inclined,  generally  away  from  the 
center,  occasionally  toward  the  center,  to  allow  the  rainwater 
to  run  off  the  road  into  longitudinal  ditches  or  gutters  in  which 
it  is  carried  to  some  convenient  point  of  egress. 

Crown. — The  raising  or  rounding  up  of  the  center  is  the 
crown  of  the  road.  The  amount  of  crowning  depends  upon  the 
character  of  the  road,  being  greater  for  road  surfaces  of  a  porous 
nature  like  earth,  than  for  those  which  are  impervious  like 
asphaltic  macadam.  Too  great  crowning  will  make  traffic 
seek  the  center,  it  being  uncomfortable  to  ride  on  the  incline. 
The  more  tracks  may  be  done  away  with  and  the  whole  road 

87 


DRAINAGE 


surface  used,  the  better.  The  crown  of  an  earth  road  may 
be  as  much  as  1  inch  to  the  foot.  An  impervious  roadway  may 
be  half  as  much.  Sometimes  the  crown  is  made  up  of  plane 
surfaces.  It  is  argued  that  a  curved  surface  is  preferable 
because  it  tends  to  distribute  more  uniformly  the  traffic  causing 

the  surface  to  wear  more 
x 

"i 


evenly,  but  the  tendency 
seems  to  be  toward  the 
plane  surface.  With  the 
plane  surface  the  fall  is 
to  the  distance-out  from  the  center. 

y  :  x::c  :  \d; 
2cx 


FIG.  38. 


directly   proportional 
Thus  in  Fig.  38 

whence, 


where  y  =  the  distance  of  the  surface  below  the  center, 
c  =  the  crown  of  the  road; 
x  =  the  distance-out  from  the  center; 
d  =  the  road  width. 

Curved  surfaces  are  most 
easily  made  the  arc  of  a 
parabola,  Fig.  39.  This 
can  be  obtained  from  the 
parabolic  formula, 

4c 

n  I  -  _   .  fffi 

y-d2  *  > 

where  the  letters  have  the  same  signification  as  above.    A  simpler 
method  is  to  consider  x  an  aliquot  part  of  the  half  road  width  ; 

that  is,  suppose  x  =  -  of  »  =  »-,  substituting  in  the  formula, 

//       _     —  // 


FIG.  39. 


=         _= 

y    d2'4n2    n2' 


ROAD   CROWNS 


If  the  depression  at  J  the  distance  from  0  to  N  is  wanted,  y  =  — ; 

ob 

c  c  9c  25 

at  \  the  distance,  —„',  at  J,  j;  at  f,  — ;  at  J,  ^c;    at  any  frac- 

4-O  ^t  JLO  oO  *    • 

k  k2 

tional  distance,  j  of  the  half  road  width,  y  =  -r^c.     These  dis- 

v  t** 

tances  may  be  measured   downward   from   a  line   stretched 
across  the  roadway  from  N  to  M  or  a  wooden  template  can  be 
made   by  rounding  out  the 
underside  or  nailing  strips  to     - 
a  board  with  ends  projecting 
below  it,  Fig.  40  (e).     With 
the  center  height  known  the 
side  stakes  may  be  obtained 
by  using  a  spirit  level  on  the 
top  of   the  board.     If   side 
grade  stakes  are  set,  the  cen- 
ter and  intermediate  stakes 


-~J> 


W) 


« 


FIG.  40.— Sight  Roads. 


can  be  quickly  set,  by  sight  rods.  Three  are  required.  They 
are  shown  in  Fig.  40. 

Rods  are  placed  upright  behind  the  stakes  at  M  and  N 
with  the  blocks  D  resting  on  their  top.  The  "  T  "  is  of  con- 
stant height  and  the  stake  upon  which  it  is  held  is  driven  until 
the  line  of  sight  from  A  to  A'  coincides  with  its  top.  Several 
notches  are  cut  in  the  rods  A,  B,  and  C  to  facilitate  setting 
intermediate  stakes.  The  top  is  used  for  center  stake,  notches  A 
for  one-fourth  distance-out;  B,  for  one-half;  and  C  for  three- 
fourths.  It  is  easier  to  sight  these  rods  if  the  farthest  one  is 
painted  white  and  the  middle  one  a  different  color. 

Side  Ditches. — The  water  having  been  shed  from  the  road 
surface  by  the  crown  must  be  further  taken  care  of.  For  this 
purpose  side-ditches  parallel  to  the  center  line  of  the  roadway 
are  constructed.  These  must  have  sufficient  longitudinal 
grade  to  allow  the  water  to  flow  along  them  until  a  place  is 
reached  where  the  natural  formation  of  the  land  will  allow  it  to 
flow  away  from  the  right  of  way.  Every  opportunity  for  this 
should  be  provided.  A  small  amount  of  water  flowing  on  to  a 


90 


DRAINAGE 


field  will  do  no  damage  but  a  large  quantity  might  be  trouble- 
some. Natural  drainage  and  water  courses  should  be  utilized 
wherever  possible.  It  is  not  generally  a  wise  plan  so  to  change 


(/•) 

Roadway  Curved  toward  the  hft 

FIG.  41. 

the  grade  of  the  road  that  water  from  one  natural  drainage  area 
will  be  carried  over  into  another.  Let  each  area  take  care  of 
its  own  water  and  thus  avoid  damage  suits. 


FIG.  42.— Wooden  Guard  Rail. 

Broad  and  shallow  ditches  are  better  than  deep  and  narrow 
ones.  They  are  not  so  dangerous  nor  are  they  so  liable  to 
become  clogged;  they  are  also  easier  to  keep  clear.  Three 


GUARD  RAILS 


91 


principal  forms  are  in  use;  the  V-shaped,  the  trapezoidal,  and 
that  in  which  the  ditch  is  a  continuation  of  the  road  surface, 
Fig.  41,  (a),  (6),  (c). 

Ditches  such  as  these  offer  but  little  obstruction  to  the  passage 
of  vehicles  over  them  whenever  necessary  or  to  the  use  of  a 
mower  to  cut  the  grass  and  weeds.  Where  the  roadway  is  on 
an  embankment  less  than  5  or  6  feet  high,  Fig.  41,  (d),  (/),  the 
slopes,  preferably,  should  not  be  steeper  than  1  :  3.  The 
ordinary  vehicle  could  go  on  this  without  tipping  over.  If  the 
embankment  is  more  than  6  feet  high  a  guard  rail  should  be  pro- 


These  bolts  fo  ex- 
tend entirely  through 

Recessj'ineach  postf 
for  attaching 


DETAIL  OF  BENT  PLATE  IN  PLACE      -  <0^' 

Corners  _rounded      .  ..  (S0 


SECTION    OF   POST 

Plate  and**}  outside  bolts 

omitted  except  at  splice  in 

rait. 

Two  washers  fobe  supplied 

with  each  bolt: 

All  bolts  3A  carriage  bolts. 


FIG.  43.— Concrete  Posts,  Wooden  Rails. 

vided  for  the  safety  of  the  traffic,  Figs.  42,  43,  44.  Frequently 
it  will  not  be  necessary  to  have  a  ditch  at  the  foot  of  the  embank- 
ment, Fig.  41,  (e),  (/).  In  a  cut  ditches  are  placed  on  the  sides 
the  same  as  on  level  ground.  On  a  side-hill  the  ditch  is  on  the 
upper  side,  Fig.  41,  (g),  (h),  (i).  Where  the  road  curves  the 
crown  should  be  brought  to  or  toward  the  outer  side  of  the 
curve,  Fig.  41,  (h),  (i}.  Side  ditches  on  slopes  can  be  paved 
in  the  bottom  to  prevent  washing.  Concrete,  brick  and  cobble 
stones  will  be  found  acceptable. 

Guard  rails,  mentioned  above  may  be  made  of  wood,  con- 
crete or  iron.     They  should   preferably  be  wide  enough  to  be 


92 


DRAINAGE 


easily  seen  and  strong  enough  to  prevent  a  vehicle  from  going 
over  if  it  should  strike  them  at  reasonable  speed.  Fig.  42  shows 
details  for  a  wooden  guard  rail;  Fig.  43,  a  combined  wood  and 


FIG.  44a. — Concrete  Guard  Rail. 

cement;  and  Figs.  44a  and  446,  a  cement.     Steel  pipes  with 
wooden  posts,  and  steel  lattice  with  steel  posts  are  also  used. 

SUB-DRAINAGE 

Where  the  subsoil  is  wet,  mucky  and  yielding,  due  to  an 
excess  of  water,  provision  must  be  made  for  under-drainage, 

else  the  "  roof "  of  the  road  will 
soon  give  way  with  consequent  rut- 
ting and  destruction  of  the  surface. 
The  methods  for  accomplishing 
this,  are  usually,  deepening  the  side 
ditches,  using  a  blind  drain,  or  lay- 
ing farm  drain  tile. 

Deep  side  ditches  are  usually  of 
the  trapezoidal  form,  Fig.  35  (a). 
With  these  open  ditches  there  is 
always  danger  of  accident;  and  they 
are  liable  to  become  clogged  with 
debris,  thus  forming  dams  which  hold  the  water  where  it  is 
not  wanted.  Open  deep  ditches  should  be  avoided  if  possible. 


FIG.  446.  —  Concrete 
Rail. 


Guard 


SUB-DRAINAGE 


93 


Blind  drains  are  made  in  a  variety  of  ways — from  a  mere  open- 
ing through  the  soil  to  the  cylindrical  farm  tile. 

A  blind  drain  plow  having  an  acorn-shaped  piece  of  steel 
at  the  bottom  of  an  extension  piece  is  drawn  through  the 
ground  to  be  drained.  It  leaves  a  small  round  opening  in  the 
soil  through  which  the  water  is  supposed  to  find  its  escape. 
Since  this  opening  may  soon  be  filled  with  earth,  it  is  not  to  be 
used  except  for  temporary  effect. 

Better  results  are  obtained  by  digging  trenches  and  par- 


Opcn  Ditch 


Stone  Slabs  Loas  and  Plank 

(«) 

FIG.  45.— Open  and  Blind  Ditches. 


tially  filling  them  writh  field  stones,  boulders,  broken  rock,  or 
gravel,  the  coarsest  at  the  bottom  and  covered  over  with  earth 
Fig.  45  (6).  In  timbered  country  logs  have  been  used  in  the 
same  manner. 

Drain  Tile. — Probably  the  best  form  of  under-drain  is  that 
made  of  clay  or  cement  drain  tile.  These  may  be  placed  under 
the  middle  or  side  of  the  road.  Under  the  side  ditch  is  con- 
sidered better  for  the  reason  that  the  road  surface  needs  not  to 
be  disturbed  for  laying  or  repairing  the  drain.  Some  good 


94  DRAINAGE 

engineers  prefer  to  have  the  drain  about  3  feet  inside  the  gutter 
in  order  that  there  may  be  no  danger  of  its  being  washed 
out  by  surface  water  running  down  the  gutter.  Tiling  will 
"  draw  "  the  water  for  a  considerable  distance  on  either  side — 
the  ordinary  estimate  being  50  feet  if  the  soil  is  reasonably 
porous.  Tile  must  be  set  carefully  to  grade  and  alignment  i 
and  deep  enough  to  avoid  the  effect  of  frost  upon  it.  In  the 
Northern  States  5  feet  is  considered  sufficiently  deep.  In  the 
Southern  States  it  should  be  covered  at  least  its  own  diameter 
to  prevent  accidental  breakage.  In  any  instance,  the  pipe 
should  be  laid  deep  enough  to  lower  the  water  table  suf- 
ficiently that  there  will  be  no  danger  of  the  road  being  broken 
through  under  the  weight  of  the  traffic.  Often  deepening  the 
pipe  on  one  side  wih1  do  away  with  the  necessity  of  tiling  the 
other  side  of  the  road  and  the  expense  may  be  much  less. 

Size  of  Tile. — The  judgment  of  experience  is  perhaps  the 
best  guide.  The  amount  of  water  which  a  pipe  will  carry 
depends  upon  its  size  and  grade;  also  on  internal  friction  and 
head  or  pressure.  Size  and  grade  are  all  that  need  to  be  con- 
sidered here.  Several  formulas  have  been  propounded  for  the 
flow  of  ;water  from  a  drainage  pipe.  Baker  1  gives  the  following : 


in  which  A  is  the  number  of  acres  for  which  a  tile  having  a  diam- 
eter of  d  inches  and  a  fall  of  /  feet  in  a  length  of  I  feet  will  remove 
1  inch  in  depth  of  water  in  twenty-four  hours. 
The  Poncelot  formula  is 


in  which  d  is  the  diameter  of  the  tile  in  feet, 

/,  the  total  fall  of  the  line  in  feet; 
L,  the  length  of  the  line  in  feet,  and 
v,  the  velocity  in  feet  per  second. 

1  "  Roads  and  Pavements/'  p.  76,  First  Edition,  5th  thousand.    Wiley 
&  Sons. 


TILE   DRAINAGE 


95 


The  Chezy-Kutter  formula,  much  used,  is, 

V  =  cVrs, 

in  which  V  =  velocity  in  feet  per  second; 

c  =  a  coefficient  found  by  Kutter's  formula; 

r  =  the  hydraulic  mean  radius; 

s  =  slope,  or  fall  in  feet  divided  by  length  in  feet; 

The  simplified  Kutter's  formula  for  obtaining  c  is 

1.811 


41.6+ 


c  — 


n 


4L6n\* 


1  + 


Spalding's  Table  for  capacity  of  tile  drains  in  cubic  feet  per 
minute  based  on  the  above  formula  with  a  coefficient  of  rough- 
ness, n  =  .013  follows : 1 


Slope  per  100 

TP--.-.J.      '„. 

OlZ-ili     U*      JTlfJU 

reet  in 
Inches 

4  in. 

6  in. 

8  in. 

10  in. 

12  in. 

2 

4.0 

12.0 

27.0 

49.5 

81 

4 

5.5 

16.5 

38.0 

70.0 

114 

6 

6.5 

21.0 

46.5 

86.5 

143 

9 

8.0 

25.5 

57.5 

106.5 

176 

12 

9.5 

29.5 

66.0 

122.5 

204 

24 

13.5 

41.5 

92.0 

173.0 

288 

36 

16.5 

51.0 

114.0 

212.0 

353 

48 

19.0 

59.0 

132.0 

245.0 

408 

60 

21.0 

66.0 

148.0 

275.0 

456 

Iowa  Highway  Commission  table:2 


1  "  A  Text-book  on  Roads  and  Pavements,"  by  F.  P.  Spalding,  Wiley 
&  Sons. 

2  Manual  for  Iowa  Highway  Officers,  1906,  p.  48. 


96 


DRAINAGE 


o o o o o      ooooo 

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ii8S8    888S8 

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rH  CO  CO  Oi  CO   Oi~CO   CO  CO 


CO  CO 

-,  ^  ^rr1  00  00  rH 

Oi  CO          to  iO  t>  b-  CO 

rHrHC<ICO-^     IO  t>  Oi  ^  O 


233528    8£8£ 

CO  ^ 


>O  1>  00  CO  "tf 

^t*  ^f  CO  »O  Oi 
CO  t^  00  C^  »O 


(N  O  -^  <M 

^  iO  »O  T1 
O5  O  i—  i  (N 


Tf  »O  Tj<  O 

T-H  Oi  <N  i—  I 


i-^COOOOS        OO  00  00  i— i  00 

1  ?P  C^  "•>  C3      Tt<  Tti  co  rH  oo 

CO  !>•  OO  Oi  Oi 


i  CO  CO  O  CO   l>- 
i  C^  t^-  tO  t^*   to 

i  r-  rH  T^l  CO     Oi 


OO  O  00 
^f  r-  (  CO 
CO 


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OSrH  C<> 


OOOOOS 


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CO 


i—  i  CO  I> 
t^r-i  >O 

CO  "*<  Tf 


itOOXNCO        OOCO'OCOb- 
ib-OCOtO        00  <— i  *  CO  00 

rHrHrH     rH(N^<N(N 


b- CO  CO  O5  to   CO  CO  »O 

O  C^  Tfl  rH  QC    Oi  GO  CO 

CO  CO  CO -^  Tj<    IO  CO  b- 


OJ  O  rH  CO  O  Is-  CO  00       •        • 

rHrHrHrHrH          rHC^OlC^CO  CO^Tf! 

C5  Oi  Oi  b-  iO        Tfi  O5  CO  CO  00  COCOON      • 

rH     rH  rH  rH  rH  i— I  C^tNC^lCO   • 

O  rH  C^l  00  rH  Oi  tO  O  rH  rH 

C^l  C^  C^  C^J  CO  CO  ^  to  CO  b* 

O  O  rH  CO  tO  O5  <N  tO  O  tO 

r-,          ^HrHrHrHrH  rH  (N  (N  CO  CO 

CO(MCO(N  COCO        CO  CO  COCO  CO 

rH  CO  rH'CO  00          T- (rH  rHOO  rHT^  rHrHQOOOrH 

rH  co  co  Oi  co   Oi  co   co~co   os  co  to  to~b- 1>  co' 

rH  rH  rH        rH 

rHrHrH     rH  rH  C<1  CO  ^  IO  b-  Oi  ^  Oi 
rH  rH 

CD?}  OOrHrHC<|  CO^tOCOl>-          OOOiOtOO  OOO«OC 

o  o  o  do     o'o  d  d  d     d  o  -I  r-1  <N 


LAYING    TILE 


97 


Roughly  speaking  tile  smaller  than  4  inches  should  not  be 
used;  it  is  difficult  to  determine  just  what  size  will  remove 
surplus  water  and  lower  the  line  of  saturation  sufficiently 
below  the  road  surface  to  prevent  trouble.  It  is  better  to  use 
tiling  too  large  than  too  small.  In  farm  drain  practice  it  is 
said,1  "  with  the  dark-silt-loam  soils  of  Illinois  and  Iowa,  where 
the  rainfall  approximates  36  inches  a  year,  an  8-inch  tile  with  a 
fall  of  2  inches  to  100  feet  will  furnish  an  outlet  for  the  complete 
drainage  of  40  acres,  a  7-inch  for  30  acres,  a  6-inch  for  19  acres, 


FIG.  46.— Staking  Out  and  Laying  Tile. 

a  5-inch  for  10  acres,  and  a  4-inch  for  6  acres.  On  stiff  soils  with 
equal  rainfall  the  same-sized  outlets  will  be  found  adequate, 
but  on  the  level  soils  of  the  South  Atlantic  and  Gulf  States, 
where  the  rainfall  is  heavier,  only  about  three-fourths  of  the 
area  can  be  drained  with  the  same  sized  tile." 

Laying  the  Tile. — To  be  of  service  the  tile  should  be  true  to 
line  and  grade.  Therefore,  the  line  of  the  ditch  should  be 
carefully  staked  and  the  grade  established.  As  much  fall  as 
possible  should  be  given;  the  faster  the  flow  of  water  the  less 
likely  is  the  pipe  to  silt  up.  A  fall  of  less  than  3  inches  to  100 

1  A.  G.  Smith,  Farmers'  Bulletin  524,  U.  S.  Dept.  of  Agri. 


98 


DRAINAGE 


feet  will  require  very  careful  leveling.  A  fall  of  3  inches  to 
100  feet  for  tile  4  inches  or  larger  will  clear  itself  of  silt  or  fine 
sand.  Short  sections  of  tile  with  frequent  outlets,  if  possible, 
will  be  found  better  and  cheaper  than  long  sections,  as  smaller 
tile  set  shallower  may  be  used. 

Having  staked  the  line  and  definitely  marked  the  grade 
(which  may  be  done  a  little  to  one  side  of  where  the  actual  dig- 
ging is  to  take  place)  cross-bars  should  be  erected  opposite  the 
stakes  over  the  line  of  the  ditch  about  every  50  feet. 

To  do  this,  drive  uprights  CF  and  DE,  Fig.  46.  With  a 
spirit  level  mark  a  line  at  C  on  a  level  with  the  grade  mark  on 


FIG.  47.— Tools  Used  for  Laying  Tfle. 

A,  usually  the  top.  Measure  up  to  a  point  F,  such  that  FC 
plus  the  cut  marked  on  the  stake  will  be  exactly  7  feet  when  the 
tile  is  to  be  laid  5  feet  deep.  Tack  the  cross-bar  FE  at  this 
point,  level  it  and  nail  at  E;  locate  H,  the  center  line  of  pipe, 
by  hanging  a  plumb-bob  along  the  bar  until  its  line  is  the  right 
distance  from  the  tack  in  A.  Drive  a  nail  at  H. 

Unless  much  ditching  is  to  be  done,  when  a  machine  may 
be  used,  the  excavating  will  be  performed  with  tiling  spades. 
These  are  from  5|  to  6  inches  wide  and  about  18  inches  long.  A 
careful  digger  can  so  use  this  spade  if  the  soil  has  the  right 
moisture,  neither  too  wet  nor  too  dry,  that  there  will  be  little 
crumbling  and  the  ditch  dug  will  be  about  16  inches  d^ep.  An 


DITCH  FILLING  99 

ordinary  shovel  can  be  used  to  remove  the  crumbs.  A  second 
spading  will  double  the  depth.  Sometimes  the  last  spade  used 
has  a  round  end,  the  spader  finishing  his  ditch  to  within  1  or  2 
inches  of  the  required  depth.  The  last  earth  is  removed  with  a 
tiling  scoop,  leaving  the  bottom  round  and  true  for  laying  the 
tile,  Fig.  47.  A  light  pole  or  rod  is  used  by  the  workman  for 
measuring  down  from  a  line  stretched  over  the  cross-bars  held 
from  slipping  sideways  by  the  nails  and  fastened  to  stakes  at 
the  side  of  the  ditch,  Fig.  46.  The  scoop  is  attached  to  the 
handle,  at  an  angle  so  that  it  can  be  used  without  standing  in 
the  ditch.  Standing  or  walking  in  the  finished  ditch  is  to  be 
avoided.  Small  tile  are  placed  in  position  by  means  of  a  hook. 
Both  digging  and  laying  the  tile  should  begin  at  the  outlet. 


S//t  Deposit 

FIG.  48. — Effect  of  Changing  Grade 

The  laying  done  as  soon  as  practicable  after  the  digging.  Extra 
work  of  cleaning  the  ditch  is  thus  avoided.  The  tile  should  be 
turned  until  the  joint  is  close  at  the  top;  large  cracks  should  be 
covered  with  broken  tile  or  canvas;  misshaped  and  cracked  tile 
should  be  discarded;  sharp  turns  and  angles  should  be  avoided; 
and  connections  made  with  "  Y's  "  and  not  "  T's."  Change 
from  a  steep  to  a  less  steep  grade  should  be  avoided  because  the 
swifter  water  on  the  steep  grade  will  carry  particles  which  will 
be  deposited  on  the  less  steep  grade,  Fig.  48. 

After  the  tile  are  laid  and  inspected,  they  are  "  primed  " 
by  cutting  off  a  little  earth  from  the  ditch  side  with  a  spade  and 
tamping  it  gently  about  the  tile  so  they  will  not  get  out  of  line. 
The  upper  end  of  a  line  of  tile  should  be  plugged  to  prevent  its 
filling  with  earth. 

Filling  the  Ditch. — The  earth  is  usually  filled  in  directly 
upon  the  tile,  but  if  the  soil  is  close-grained  or  compact  drainage 


100 


DRAINAGE 


may  be  assisted  by  putting  in  first  some  porous  material,  such 
as  broken  rock,  brick  or  gravel.  However,  in  most  soils  this  will 
not  be  necessary  as  the  water  will  eventually  carve  out  runways 
for  itself;  the  drainage  of  a  line  of  tile  improves  with  age. 

A  plow  attached  to  a  long  evener  so  that  one  horse  may 
walk  each  side  of  the  ditch  can  be  efficiently  used.     The  ditch 


FIG.  49. — Outlet  Protection. 

can  be  filled  with  a  team  and  scraper.     Filling  by  hand  is,  of 
course,  possible,  but  much  more  expensive. 

Outlets. — The  outlet  of  a  line  of  pipe  should  always  be  pro- 
tected, Fig.  49.  A  concrete  wall  makes  the  best  comparatively 
cheap  protection.  Stone,  brick  and  timber  may  also  be  used. 
Or  a  long  section  of  corrugated  galvanized  iron  pipe  will  stick 
out  far  enough  to  prevent  caving  under.  Wire  netting  can  be 


FIG.  50.— V-Drain 

used  to  prevent  small  animals  from  entering.  If  the  mouth 
becomes  submerged  a  valve  may  be  provided  to  prevent  the 
water  and  silt  from  backing  into  the  drain. 

V-Drains. — Sometimes  V-drains  are  constructed  under  the 
center  of  a  road  by  excavating  a  V-shaped  trench  ABCDE, 
Fig.  50,  and  partially  filling  it  with  boulders,  field  stones, 
broken  rock,  or  gravel.  The  earth  may  be  pushed  over  to  the 
shoulders  of  the  road,  by  loosening  with  a^plow  and  using  the 


V-DRAINS.    WATER  'COURSES  101 

blade  grader.  Stones  not  exceeding  12  inches  in  diameter  are 
placed  in*  the  bottom  of  the  excavation,  with  the  largest  stones 
under  the  center,  diminishing  toward  the  sides.  These  are 
rolled  and  the  drain  completed  by  smaller  stones  and  coarse 
gravel  on  top,  the  surface  being  parallel  to  the  finished  roadway. 
Before  final  surface  material  is  applied  suitable  outlets  DF, 
Fig.  50,  should  be  built  through  the  shoulders  at  intervals  of 
not  more  than  200  feet,  and  especially  to  low  points  where  the 
water  may  drain  from  the  right  of  way.  These  outlets  are 
filled  with  stone  and  gravel  about  3  feet  wide  and  deep  enough 
to  permit  the  escape  of  the  water  from  the  V-drain. 

Where  stones  suitable  for  building  V-drains  are  not  available 
coarse  clean  gravel  may  be  used  and  a  4-inch  land-tile  pipe 
placed  at  the  bottom.  Outlets  are  made  by  using  Y's  and  the 
same  sized  tile.  Outlets  should  preferably  not  be  at  right 
angles  to  the  roadway  but  diagonally  down  to  the  grade.  The 
joints  of  drain-tile  thus  used  should  be  wrapped  with  canvas 
or  burlap  to  prevent  the  entrance  of  fine  sand  or  silt. 

Draining  Ponds. — Lines  of  tiling  placed  in  the  pond  give 
best  results.  Wells  bored  in  the  pond  through  the  impervious 
bottom  to  porous  subsoil  have  been  found  to  be  temporarily 
effective. 

Water  Courses. — It  will  sometimes  be  advisable  to  turn  a 
water  course  to  save  the  building  of  a  bridge  or  bring  it  to  a 
safer  or  more  convenient  position.  The  size  of  such  ditch  can 
ordinarily  be  judged  by  the  size  of  the  original  water  course, 
remembering  that  if  the  stream  be  straightened  the  grade  will 
be  steeper  and  the  water  run  faster.  If  the  area  of  the  land 
drained  through  this  ditch  is  known  the  table  heretofore  given 
in  this  chapter  will  assist  in  ascertaining  the  size. 

The  quantity  of  earth  excavated  from  such  ditches  may  be 
calculated  by  averaging  end  sections  just  as  is  done  in  figuring 
quantities  in  embankment  and  in  excavations. 

Resume. — It  must  be  remembered  that  the  object  of  drain- 
age is  to  remove  the  water  from  the  roadway  so  quickly  that  it 
will  not  soften  the  surface.  This  is  accomplished  by  crown  and 
side  ditches.  The  water  plane  beneath  the  roadway  must  be  so 


>t-  I' 

102  DRAINAGE 

far  from  the  surface  that  the  "  roof  "  of  the  road  will  not  break 
in.  In  most  places  this  will  be  so  naturally  and  no  special 
under-drainage  will  be  necessary.  If  the  natural  condition 
of  the  subsoil  is  not  sufficiently  dry  provision  must  be  made  for 
sub-drainage,  or  for  raising  the  surface  by  grading  above  the 
waterplane.  An  embankment  thrown  up  through  a  short  valley 
will  in  addition  to  accomplishing  this  object  often  reduce  the 
gradient  of  the  road.  Good  judgment  based  upon  local  con- 
ditions surrounding  the  particular  case  in  hand  must  always 
be  exercised. 


CHAPTER  V 
CULVERTS  AND  BRIDGES 

MOST  of  the  States  have  highway  departments  which  pre- 
pare standard  plans  and  specifications  for  culverts  and  bridges. 
Where  these  are  obtainable  they  should  be  used.  In  this 
chapter,  therefore,  only  a  few  plans  will  be  submitted ;  nor  is  it 
the  intention  to  go  into  detail  of  methods  of  calculating  stresses 
in  such  structures. 

Definition. — Originally  the  word  culvert  was  applied  to  a 
small  covered  drain  or  water  way  under  a  road,  street  or 
canal,  while  bridges  were  structures  built  over  streams,  streets, 
or  canals.  Now  the  term  culvert  seems  to  be  applied  to  the 
smaller  of  such  structures,  and  bridges  to  the  larger;  where  one 
ends  and  the  other  begins  is  not  very  definitely  defined.  The 
Colorado  Highway  Commission  says,  "  Clear  spans  of  10  feet 
and  over  are  referred  to  as  bridges;  all  under  10  feet,  as  cul- 
verts." 1  The  Wisconsin  Highway  Commission  classifies  all 
waterway  structures  6  feet  and  under  as  culverts.  It  might 
be  well  to  make  16  feet  the  dividing  line. 

Size  of  Waterway. — The  size  of  the  opening  under  a  bridge 
or  through  a  culvert  is  usually  spoken  of  as  the  area  of  the  water- 
way. In  determining  this,  first,  existing  openings,  -if  there  are 
other  bridges  upon  the  same  stream,  should  be  observed; 
second,  evidences  of  high  water  such  as  drift,  and  the  testimony 
of  residents  should  be  taken;  third,  formulas  for  openings  may 
be  applied  "  as  a  guide  to  judgment  "  after  noting  the  char- 
acter of  the  topography  of  the  country,  area  drained,  heaviest 
rainfall,  and  peculiar  local  conditions.  Sometimes,  though  not 
considered  the  best  practice,  the  water  may  be  allowed  to  dam 
1  Bulletin  No.  4,  Colorado  State  Highway  Commission. 
103 


104 


CULVERTS  AND   BRIDGES 


up  back  of  a  culvert,  the  increased  pressure  thus  obtained 
hastening  the  flow  of  the  water.  Care  must  be  taken  that  this 
will  not  damage  the  highway  or  surrounding  property.  It  may 
not  always  be  wise  to  provide  for  extreme  cases  of  high  water 
that  have  occurred  only  once  in  a  generation;  it  may  be  cheaper 
to  risk  the  washing  out  of  a  road  or  culvert. 

Fig.  51  is  a  plot  of  Talbot's  formula  for  the  area  of  water- 
ways, which  is 

Area  i n  square  feet  =  CSX (drainage  area  in  acres)3  in  which 
C  is  a  constant  depending  on  the  slope,  varying  from  £  to  2. 


1020304050  02408    10 

Size  of  Opening,  Square  Feet 

FIG.  51. — Talbot's  Formula  for  Waterway  Openings. 

The  Burlington  railway  for  the  so-called  Prairie  States  uses 
the  McMath  formula  in  this  form: 

Area  in  square  feet  =  0.20625^15  (drainage  area  in  acres)4 
for  a  drainage  area  of  less  than  640  acres;  when  the  area  is 
more  than  640  acres  the  formula. 

A        .                 f          300  (drainage  area  in  sq.  mi.)1 
Area  in  square  feet  =  —       '    "  M        - — . 

3+2(v  drainage  area  in  sq.  mi.) 
Design. — The  design  of  the  bridge  or  culvert  must  be  suit- 

1  For  a  digest  of  this  subject  see  Proceedings  Am.  Ry.  Eng.  Assn., 
Vol.  XII,  Part  3,  page  470. 


WATERWAYS 


105 


able  for  the  location  and  its  character  will  depend  upon  local 
conditions  as  to  traffic,  desires  of  users  and  other  considerations. 
For  very  large  bridges  a  competent  engineer  should  be  con- 
sulted. It  is  not  the  intention  here  to  enter  into  the  discussion 
of  such  structures. 


TEMPORARY  AND  EMERGENCY  STRUCTURES 

Where  traffic  will  not  warrant,  nor  time  permit,  where 
materials  are  not  available  for  more  permanent  structures, 
temporary  culverts  and  bridges  must  be  built. 

Wooden  Box  Culverts. — Two  plans  for  these  are  sketched. 


FIG.  52.— Plank  Culvert. 


FIG.  53.— Wooden  Box  Culvert.  Up  to  4' 
Square,  2"X4"  Stiffening  Forms  and 
2"X12"  Plank  are  Suitable. 


Fig.  52.  Made  of  2Xl2-in.  plank  nailed  together,  giving  a 
10X12  opening. 

Fig.  53.  This  box  culvert  can  be  made  any  size  by  using  a 
proper  number  of  stiffening  forms.  As  illustrated  it  i&  built  of 
2  X  12-inch  plank  and  2X4-inch  forms.  The  forms  should  be 
spaced  from  2  to  3  feet  apart  and  the  planks  well  nailed  that 
the  pressure  of  the  earth  may  not  push  them  off. 

High- water  Low  Bridge. — Sometimes  when  a  bridge  is  out  of 
commission  it  is  necessary  to  put  in  a  temporary  bridge  to 
accommodate  traffic  until  the  regular  bridge  can  be  repaired. 
A  low  bridge  under  which  all  the  water  cannot  pass  in  case  of  a 
hard  rain  can  quickly  and  easily  be  made  by  throwing  two  or 


106 


CULVERTS  AND   BRIDGES 


more  stringers  across  the  stream  and  nailing  some  plank  on 
them.  If  the  up-stream  side  of  the  bridge  be  made  about  6  or  8 
inches  lower  than  the  down-stream  side  the  pressure  of  the  water 
when  it  flows  over  the  bridge  will  prevent  it  from  going  out. 
As  a  precautionary  measure,  solid  stakes  should  be  driven  at  the 
ends  of  the  stringers  and  these  securely  wired  or  nailed  to  them. 
If  long  stakes  are  set  to  show  the  position  of  the  roadway,  this 
bridge  may  be  used  as  a  ford  in  case  of  high  water. 

Pile  and  Stringer  Bridge. — This  is  a  common  type  of  bridge 
in  the  Middle  West.     The  trestles  are  made  by  driving  four 


«'fc 


Guard  Rail  Fastened  to  Floor 
•  Blocks       \  through  filler  Block 


>3*x  12  strtti  eppotitt 
(Handrail  post  \ Strut" C   ^      f 


2  <  2  Bridging  one  set 

2*x  6  "Guard 


Elevation 


u  posts 
tontmuej  doun  a 
spiked  to  tap 


T^^TOTO.. 

Pott  U'lef.rmly 
set  in  ground  and 
'  bolted  or  wireJ.  to 


Cross  Section 


FIG.  54. — Pile  Highway  Bridge  after  Plan  by  Iowa  Highway  Commission. 


piles  in  line  across  the  road  space,  sawing  them  off  at  exact  ele- 
vation, and  fastening  on  a  cap  of  heavy  timber  with  driftbolts.  ' 
Joists  are  then  placed  from  trestle  to  trestle  and  the  planks 
nailed  thereto.  This  is  finished  with  a  guard  rail.  When  the 
piling  are  exposed  for  a  distance  of  8  feet  or  more  they  should 
be  sway-braced  by  bolting  two  2  X  10-inch  planks  to  the  piles. 
If  the  diagonal  distance  from  cap  to  ground  is  more  than  18  feet, 
two  or  more  sets  of  sway-bracing  should  be  used,  Fig.  54. 

The  bearing  power  of  piling  may  be  obtained  by  the  common 
formula 

2Wh 
Safe  load  in  pounds  =  -0-7^  • 


BEARING  POWER    OF  PILING  107 

in  which  W  represents  the  weight  of  pile  driver  hammer  in 
pounds; 

h,  the  fall  of  the  hammer  in  feet; 

s,  the  average  penetration  of  the  pile  in  inches  the  last  three 
or  four  blows. 

EXERCISE 

Find  the  safe  load  of  a  pile  which  is  lowered  \  inch  by  a  20-foot  fall  of 
a  1500-pound  hammer.  _  Ans.  20  tons. 

White  oak  and  red  cedar  piling  are  considered  to  be  best; 
for  floors,  oak  or  fir;  other  parts,  fir,  spruce,  or  yellow  pine. 
Timber  should  be  uniform  in  quality,  sound,  free  from  large 
season  checks,  heart  shakes,  or  large  loose  knots.  When  such 
bridges  are  more  than  30  feet  high  the  cost  of  the  necessary 
long  piling  becomes  excessive. 

i 

MOBE  PERMANENT  STRUCTURES 

i- 

!  Cast-iron,  wrought-iron,  "  ingot  iron  "  and  low-carbon  low- 
i  manganese  steel  are  used  for  road  culverts. 
j  Cast-iron  is  made  up  in  different  forms.  Fig.  55  shows 
four  kinds  of  cast-iron  culverts.  Cast-iron  makes  a  very  dura- 
ble culvert  and  were  it  not  for  high  cost  of  freight  due  to  its 
weight  would  be  much  more  extensively  used. 
j  Corrugated  Iron  and  Steel  Plate. — Many  culverts  such  as 
•'shown  in  Fig.  56  are  now  in  use.  Corrugating  the  plate  stiffens 
it  so  that  if  covered  with  earth  to  the  depth  of  the  diameter 
of  the  pipe  it  will  sustain  any  ordinary  load.  Where  these  are 
made  up  of  wrought  iron,  "  ingot  iron  "  or  low-carbon  Jow^ 
manganese  steel,  they  will  last  indefinitely.  Should  one  ever 
show  signs  of  rusting  through,  it  may  be  used  as  a  form  for 
building  a  concrete  pipe  over  and  around  it.  Steel  which  has  a 
high  percentage  of  carbon,  manganese  or  any  other  impurity 
should  not  be  used  as  a  culvert,  for-  it  will  soon  corrode.  Cor- 
rugated iron  culverts  are  comparatively  light,  so  by  making 
them  up  in  sections  and  nesting  them  a  great  many  feet  may 
be  placed  in  a  car  load.  Fig.  56  shows  various  kinds. 


108 


CULVERTS  AND  BRIDGES 


FIG.  55. — Cast-iron  Culverts. 


FIG.  56. — Sheet-metal  Culverts. 


PIPE   CULVERTS 


109' 


The  outlet  end  of  all  pipe  culverts  should  be  carefully 
protected  if  there  is  any  likelihood  of  washing.  Boulders,  logs, 
planks,  concrete  are  some  of  the  means  of  protection. 

Vitrified  Clay  Pipe. — The  formula  given  by  the  Iowa  State 
College  l  for  the  weight  of  the  filling  on  a  drain  tile  and  the  spe- 
cifications of  drain  tile  by  the  American  Society  for  Testing 
Materials  2  may  be  used  for  pipe  culverts.  Fig.  57  shows  the 
ordinary  supporting  strengths  of  drain  tile  necessary  for  the 

Depth  of  Filling,  Feet  above  Tile  _ 


2000 


6000 


=  8000 


10000 


12000 


14000 


2ft.   2770 


6230 


4   :» 

9 


oft. 


17300 


FIG.  57. — Standard  Ordinary  Supporting  Strength  of  Drain  Tile  Wet  Clay 
Filling  Material. 

depths  and  widths  of  ditches  given.  The  seller  of  pipe  should 
guarantee  that  they  will  comply  with  A.  S.  T.  M.  specifications. 

In  laying  the  pipe  the  socket  end  is  toward  the  inlet  and  the 
bell  toward  the  outlet.  The  joints  may  be  cement  filled  to 
prevent  water  leaking  through  and  softening  the  foundation. 

Cement  Pipe. — These  are  used  the  same  as  clay  or  cast  iron 
and  of  coarse  must  stand  the  same  loads.  Large-sized  cement 
pipes  usually  have  their  ends  beveled  so  they  will  fit  into  each 

1  Iowa  State  College  Engineering  Experiment  Station  Bulletins  Nos. 
31  and  34. 

2  A.  S.  T.  M.  Standards,  1916,  p,  452. 


110 


CULVERTS  AND   BRIDGES 


other,  the  better  to  maintain  alignment.  The  larger  sizes 
should  be  reinforced  with  steel  bars.  Several  kinds  of  forms 
for  making  cement  pipes  are  on  the  market.  Some  counties 
are  employing  their  indigent  men  to  manufacture  the  pipes 
during  the  winter  months.  By  summer  the  pipes  have  cured 
and  are  ready  to  be  hauled  to  place  and  set  in  the  roadway. 
Concrete  pipe  should  not  be  used  where  there  are  large  quan- 
tities of  alkaline  salts  that  have  a  tendency  to  disintegrate 
Portland  cement  concrete. 

Twin  Pipe  Culvert. — When  one  pipe  is  not  large  enough  to 
convey  all  the  water  another  may  be  installed  beside  it  making 
a  twin  pipe  culvert,  the  end  protection  being  lengthened  accord- 
ingly. 

Foundation. — It  is  essential  that  all  types  of  culverts  have 


FIG.  58.— Culvert  End  Protection. 

good  foundations.  Where  the  soil  is  mucky  or  soft  a  con- 
crete bed  extending  about  one-fourth  the  height  of  .the  pipe  is 
recommended.  Back-filling  should  be  carefully  tamped  in 
about  the  pipe  to  prevent  undue  settlement. 

End  Protection. — Head  walls  are  more  important  with  jointed 
clay  and  concrete  pipes  than  with  long  corrugated  or  cast-iron 
pipes.  Fig.  58  shows  forms  of  head  and  wing  wall  protec- 
tion. 

Where  the  embankment  above  a  culvert  is  not  great  the 
head  wall  may  be  built  parallel  to  the  line  of  the  road.  WTiere 
there  is  an  embankment,  the  length  of  the  culvert  may  be  cut 
down  by  building  wing  walls.  Economy  and  space  for  water 
will  often  determine  which  should  be  used.  Concrete  lends 
itself  well  to  the  building  of  such  protection  heads;  brick, 
stone  or  wood  may  also  be  used  with  success. 

Intake  Drop. — Where  it  is  difficult  to  get  sufficient  depth  of 


BOX  CULVERTS 


111 


roadway  over  the  culvert,  or  the  conformation  of  the  ground 
demands  the  culvert  is  sometimes  dropped  and  an  intake  con- 
structed on  the  upper  end.  This  is  an  open  box  of  concrete 
or  masonry  and  is  not  difficult  to  make,  Fig.  59. 

Box-culverts. — A  small  culvert  having  a  rectangular  opening 


FIG.  59.— Intake  Drop.  FIG.  60.— Stone  Box  Culvert. 

is  called  a  box-culvert.  Most  any  material  or  combinations  of 
materials  may  be  used  for  such  culverts.  Already  wooden 
types  have  been  shown,  Figs.  52  and  53. 

Where  stone  of  suitable  kind  is  plentiful,  small  culverts 
may  be  built  as  shown  in  Fig.  60.     Masonry  walls  are  built 


/-~ Parapet  Walls 


Hand  Hall  - 


I-beams,  15  inch  43  Ib. 

Expanded  metal 

Concrete  or  stone  abutments 


FIG.  61. 

I-beam  Culvert.     Eight  15-inch  43-lb.  I-beams,  27  ft  long,  will  be  needed  for  a 
24  ft.  span.     Expanded  metal  reinforcing  to  be  used  above  the  beams. 

upon  each  side  and  capped  by  large  flat  stones.  The  thickness 
of  the  cap  stones  should  not  be  less  than  12  inches  for  openings 
of  4  feet.  Since  large  cap-stones  are  often  difficult  to  obtain, 
reinforced  concrete  slabs  have  been  used  for  this  purpose. 
Rubble  masonry  or  concrete  walls  may  be  spanned  by  steel 


112 


CULVERTS  AND   BRIDGES 


I-beams  to  support  a  thin  concrete  slab  for  floor,  Fig.  61. 
In  Ne\v  York  State  such  slabs  are  made  6  inches  thick.  The 
weight  of  the  roof  and  load  is  carried  by  the  I-beams.1 


Half  E leoatioa  '     Half  Stctiun 
FIG.  62. — Concrete  Box  Culvert. 

Concrete  Box  Culverts. — Nearly  every  State  has  its  standard 
forms  for  concrete  box  culverts.  Fig.  62  shows  a  typical 
form  after  a  plan  prepared  by  the  U.  S.  Office  of  Public  Roads. 

&$*&&^\?.$'*y; : X  \^^^^^^m^  • -^^^^i^^Mir  "I 

7  P^iM^^^^^^^^^^^^^§^^^M  ? 


S^»are.  72  C  to  C  or  V  /?oi/nrf,  10  CtoC 
^S=  Span 


FIG.  63.— Reinforced  Concrete  Slab  Culvert,  Floor  Dimensions. 

Fig.  63  and  table  following  show  the  thicknesses  and  other 
dimensions  of  floor  slabs.  The  data  and  calculations  are  from 
the  publications  of  the  office  of  Public  Roads,  U.  S.  Depart- 
ment of  Agriculture. 

1  For  descriptions  of  I-beam  and  other  culverts,  see  U.  S.  Depart- 
ment of  Agriculture  Bulletins:  No.  43,  /'Highway  Bridges  and 
Culverts";  No.  45,  "Data  for  Use  in  Designing  Culverts  and  Shorts-pan 
Bridges." 


CONCRP]TE   CULVERTS 


113 


REINFORCED  CONCRETE  FLOOR  SLAB  DIMENSIONS 

Assumed  Data:  1:2:4  Concrete;  Deadload  700,  Live  Load  470  Ib. 
per  Sq.  In.,  Modulus  of  Elasticity:  Concrete,  900,000,  Steel,  30,000,- 
000  Ib.  Per  Sq.  In. 


THICKNESS,  INCHES 

LENGTHWISE  REINFORCING 

Span, 

RODS,  INCHES 

feet 

T 

U 

Square 

Spacing 

Round 

Spacing 

2 

6 

*i 

ft 

8 

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6 

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7 

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5 

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6 

6 

9 

71 

f 

7 

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8 

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8 

f 

6^ 

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9 

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5| 

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5 

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DETAILED  METHOD  OF  CONSTRUCTING    CONCRETE    CULVERT 

These  culverts  are  especially  adapted  to  flat  country  where 
the  head  room  for  arches  cannot  easily  be  obtained. 

The  wooden  forms  for  their  construction  are  simple,  Fig.  64. 
Two-inch  lumber  dressed  on  the  face  side  and  edges  should  be 
used  for  the  sides  and  top.  If  a  small  trench  is  dug  the  earth 
may  be  used  for  the  outside  form,  otherwise  boards  may  be 
set  up  and  braced  to  position.  These  may  be  given  a  batter  if 
desired. 

The  bents  may  be  made  of  2X4's  nailed  firmly  together 
and  placed  3  feet  c.  to  c.;  2X6's  are  well  adapted  for  sides  and 


114 


CULVERTS  AND   BRIDGES 


cover.  Only  a  few  nails  and  these  in  small  sizes  should  be 
used  in  the  boards  on  the  sides.  Tops  will  need  none  what- 
ever. Centering,  of  course,  should  be  made  strong.  The 
wedges  should  be  of  hard  lumber,  smoothed.  After  the  forms 
are  braced  and  blocked  in  position,  they  may  be  painted  with 
oil  or  greased  with  soap  or  hard-oil;  this  will  prevent  the  con- 
crete from  sticking,  facilitate  the  removal  of  the  forms  and  give 
a  smoother  and  better  appearance  to  the  work. 

The  concrete  should  be  deposited  with  care,  so  that  the 
aggregate  and  mortar  will  not  separate,  and  spaded  thoroughly 


Ber.^every  other  rod  upatX  'span  SPlanh 

'2x  4 Spaced 
3ft.  on  centers 


i$x$*>--.y«    ^^r  -  ,ov  'V-:^ V::     Q     ;(^-"'"T 
I^~^=&S^^^$ 
..  SSsJ::.;b     :'o:::°. 


rerr.oving  boards 

FIG.  64.— Box  Culvert  Forms. 

against  the  forms.  A  flattened  shovel  or  a  broad  sharpened 
chisel  shaped  on  one  side  may  be  used  for  this  by  pushing  it 
down  next  the  plank  and  prying  the  coarse  aggregate  away  from 
the  form.  The  concrete  should  be  plastic  and  tamped  until  it 
quakes.  Some  engineers  prefer  a  slushy  mixture  so  that  it  will 
flow  "to  place,  especially  is  this  true  if  reinforcing  rods  are  to  be 
used.  This  is  not  recommended  because  excess  water  weakens 
concrete.  In  placing  the  concrete  it  is  well  to  carry  it  up 
equally  at  all  parts  in  order  that  the  water  will  not  drain  off  and 
take  with  it  the  cement,  and  that  stresses  may  be  equalized. 
If  it  is  impossible  to  do  this  the  work  should  be  divided  into 
sections  and  each  section  completed  without  interruption. 


DEPOSITING  CONCRETE  115 

Vertical  joints  which  will  key  into  each  other  should  be  pro- 
vided at  the  ends  of  the  sections.  This  may  be  done  by  insert- 
ing a  piece  of  4-inch  timber  6  or  8  inches  wide  against  the 
end  wall  and  withdrawing  it  after  the  concrete  has  set  and 
before  beginning  the  next  section.  Whenever  the  depositing 
of  concrete  has  been  interrupted  the  surface  of  the  old  concrete 
should  be  thoroughly  wetted  and  a  grout  of  water  and  cement 
mixed  to  a  creamy  consistency  applied  just  before  depositing 
the  new  concrete.  Any  "  laitance,"  a  whitish  or  yellowish 
deposit  of  fine  particles  of  cement  or  silt  separated  from  the 
concrete  of  the  previous  work,  must  be  removed  in  order  to 
secure  a  proper  bond. 

To  remove  the  forms  the  wedges  can  be  loosened;  the  cen- 
tering, roof  and  sides  will  easily  slip  out.  Forms  should  be  left 
in  until  the  concrete  has  hardened  sufficiently  to  carry  the  loads 
that  may  come  upon  it.  Twenty-eight  days  is  considered  a 
reasonable  time  for  structures  of  considerable  size.  The  forms 
may  be  removed  from  small  culverts  at  a  shorter  period.  In 
removing  forms  great  care  should  be  exercised  not  to  break  off 
corners  or  projecting  parts.  Tapping  or  slipping  the  boards 
endwise,  where  that  may  be  done,  will  prevent  sticking  and 
scaling  or  slabbing  off.  In  panel  work  and  other  irregular 
surfaces  extreme  care  should  be  exercised  in  greasing  the  forms 
before  depositing  the  concrete. 

Head  and  Wing  Walls. — For  small  culverts  a  protecting 
wall  is  usually  erected  parallel  to  the  roadway  of  such  length 
as  may  be  thought  necessary.  The  length  will  depend  upon  the 
height  and  character  of  the  embankment,  as  well  as  the  size  of 
the  culvert. 

Slab-bridges. — When  the  span  is  lengthened  on  such  cul- 
verts as  last  mentioned  they  become  slab-bridges.  For  spans 
up  to  20  feet  the  flat  type  of  slabs -is  applicable.  They  are 
economical  to  construct  and  furnish  a  bridge  well  adapted  to 
the  more  or  less  level  country  of  the  Prairie  States.  The  water- 
ways are  adequate  and  the  horizontal  lines  blend  in  with  such 
landscapes  admirably.  The  side  walls  of  the  bridge  besides 
forming  parapets,  also  are  used  as  girders  to  strengthen  it. 


116 


CULVERTS  AND   BRIDGES 


Fig.  65  shows  the  standard  designs  for  slab  culverts  and  bridges 
adopted  by  the  Virginia  State  Highway  '  Commission.  The 
accompanying  table  gives  the  amount  of  reinforcement  used  in 
these  bridges. 

Arch  Culverts.  —  The  arch  furnishes  a  type  of  bridge  or 
culvert  which  is  extremely  attractive;  when  properly  made  is 
strong  and  durable  and  has  a  large  opening  for  the  discharge 
of  water.  It  is  especially  appropriate  in  deep  depressions  or 


" 


Longitudinal  Section 


A. 


Tok  Slab  Reinforcement 


Cross  Section 


FIG.  65. — Typical  Reinforced  Concrete  Slabs  for  Highway  Culverts,  Office 
of  State  Highway  Commission,  Richmond,  Va. 

ravines  or  under  high  fills  on  account  of  abundance  of  head 
room.  Here,  too,  it  harmonizes  well  with  the  landscape.  The 
arch  culvert  should  only  be  erected  on  the  best  of  founda- 
tions for  any  yielding  there  will  loosen  the  parts  and  destroy 
the  arch.  Stone  and  brick  have  long  been  used  for  such 
culverts.  Of  late  years  concrete  has  largely  superseded  these 
materials  on  account  of  its  conformability  to  local  condi- 
tions, its  comparative  cheapness  and,  in  the  reinforced 
variety,  its  ability  to  withstand  tensile  as  well  as  compressive 
stresses. 


FLOOR  SLAB   TABLE 


117 


i 

g 

I 

O 

^ 

S 

s 

PQ 
EH 


PAR 
REINFO 


TRANSVERSE 
REINFORCEMENT 


S 


TO  A 
REINFORCE 


Ijj 


Concrete 
Cu.  Yds. 


GO 
CO 


,-Ti<l>O 

rH     rH    rH    (N 


oooooooooo 


OOGOOOOOGOOOOOCXDOOCX) 


£8 


OOOOOOOOOO 


cooocoeococococoooco 


cOlOOtOiOOiOlOlO 
INCOCOCOCOCOCOCOCO 


8£ 


- 


—  c     3     fcC 


02 


*« 


» -f  *  J  ^ 


S  «  •£ 

g  03      g 

I  S,-0 

a  g  ^ 


118 


CULVERTS  AND  BRIDGES 


CULVERT  FORMS  119 

Fig.  66  shows  a  form  of  arch  culvert  designed  by  the  U.  S. 
Office  of  Public  Roads,  Bulletins  Nos.  39  and  43.  For  this 
culvert  the  following  quantities  will  be  required: 

Concrete,  arch  and  parapets  (1:2:4) 12.9  cu.  yds. 

Concrete,  side,  end  and  wing  walls  (1  :  2|  :  5) 39.8  cu.  yds. 

Concrete,  footing  (1:3:6) 20.1  cu.  yds. 

This  will  take 

102  barrels  cement. 
33  cubic  yards  sand. 
66  cubic  yards  stone  or  gravel. 

If  a  floor  is  wanted  below  the  waterway  the  material  for 
this  must  be  added,  and  mixed  the  same  as  the  footings.  The 
footing  and  floor  concrete  should  be  deposited  first  and  the  forms 
for  the  arch  erected  on  this. 

Forms. — Fig.  67  shows  a  method  of  placing  the  centering 
for  n,  concrete  arch  bridge.  This  must  be  well  and  strongly 
made  for  much  weight  will  come  on  it  while  the  concrete  is 
green.  The  ribs  in  Fig.  67  are  spaced  every  4  feet,  supporting 
2  X  6-inch  lagging,  and  rest  upon  wooden  posts.  The  wedges 
are  hard  wood  and  smooth.  Safe  removal  of  the  centering 
depends  upon  the  proper  driving  of  the  wedges.  Spandrel 
and  guard  rail  forms  may  be  built  at  the  same  time  that  the 
arch  ring  centering  is  placed.  To  prevent  the  concrete  sticking 
to  the  forms  they  should  be  treated  with  a  coating  of  soap  or 
grease. 

Removing  Forms. — In  striking  the  centers,  the  wedges  under 
the  crown  should  be  removed  first,  in  order  that  the  strains 
may  be  equalized  under  the  two  sides  of  the  arch.  The  arch 
centers  should  be  left  in  place  until  the  concrete  is  sufficiently 
hard  to  hold  its  weight  and  that  of  the  superimposed  roadway 
and  will  not  chip  or  crumble  in  removing  the  forms.  The 
Iowa  Highway  Commission  requires  a  minimum  time  of  three 
weeks.  The  Portland  Cement  manufacturers  think  it  should 
not  be  less  than  four  weeks  in  good  drying  weather,  and  longer 
in  cold  or  wet  weather,  the  latter  being  unfavorable  to  the 
hardening  of  the  concrete. 


120 


CULVERTS  AND  BRIDGES 


Fig.  68  shows  a  plain  culvert,  somewhat  between  an  arch 
and  a  box,  designed  by  the  Minnesota  Highway  Commission. 
There  is  an  accompanying  table  of  dimensions. 


ELEVAT/ON 


BOTTOM  VIEW 
CENTERING  FOR  CONCRETE  SEMICIRCULAR   BRIDGE 

FIG.  67. — Cross-section. 


Guard  Rails  and  Parapets. — It  is  becoming  quite  popular 
to  run  the  concrete  sidewall  above  the  culvert  far  enough  to 


GUARD   RAILS  AND   PARAPETS 


121 


TABLE    OF    DIMENSIONS    FOR    PLAIN    MINNESOTA    (ARCH) 

CONCRETE  CULVERTS. 

Sizes  2X2  Feet,  to  4X4  Feet, 


w 

# 

A 

:* 

c 

Z) 

1 

,_ 

7 

K 

M 

* 

71 

2'    0" 

2'    0" 

1'    0' 

0'      8^' 

r  2' 

5'    5" 

3'    0" 

1'      2" 

0'    6" 

0'      6" 

0'    8" 

0'    8" 

0'      8" 

2'    0" 

2'    6" 

1'    0' 

0'      8i' 

1'    2' 

5'    3" 

3'    6" 

1'      4" 

0'    6" 

0'      7" 

0'    8" 

0'    8" 

0'      8" 

2'    6" 

2'    6" 

1'    2' 

0'      9i' 

I'    3' 

6'    5" 

3'    6" 

1'      5" 

0'    6' 

0'      7" 

0'    8" 

0'    8" 

0'      9" 

2'    6" 

3'    0" 

V    2' 

0'      9J' 

1'    3' 

6'    5" 

4'    0" 

1'      7' 

0'    6' 

0'      8" 

0'    8" 

1'    0" 

0'      9" 

3'    0" 

3'    0" 

I'    4' 

0'    10*' 

1'    4' 

7'    5" 

4'    0" 

1'      8' 

0'    7' 

0'      8" 

1'    2" 

i'  o" 

0'    10" 

3'    0" 
3,    6" 

3'    6" 

y  6" 

r  4' 

1'    6' 

0'    11J' 

1'    5' 

8'    5" 

4'    6" 

1'    11' 

0'    7' 
0'    7' 

0'      9" 
0'      9" 

1'    2" 
1'    2" 

1'    0" 
1'    4" 

0'    10" 
0'    11" 

3'    6" 

4'    0" 

1'    6' 

0'    Hi' 

1'    5' 

8'    5" 

5'    0" 

2'      1' 

0'    7' 

0'    10" 

1'    2" 

1'    2" 

0'    11" 

4'    0" 

4'    0" 

1'    8" 

r   or 

1'    6" 

9'    5" 

5'    0" 

2'      2' 

0'    8' 

0'    10" 

1'    2" 

1'    8" 

1'      0" 

'face  of  Roadway 


CROSS  SECTION 


FIG.  68. — Concrete  Culverts  Designed  by  the  Minnesota  State  High- 
way Commission. 

furnish  a  guard  rail.  Some  of  the  plans  show  this.  Paneling 
these  parapets  helps  the  esthetic  features  of  the  bridge.  The 
parapets  also  serve  in  flat  slab  construction  as  girders. 

Gas-pipe  guard  rails  are  also  used.  These  are  made  up, 
set  in  the  forms  and  cast  into  the  concrete  of  the  side  walls. 
Objection  is.  made  to  pipe  rails  on  account  of  weakness  and  lack 
of  visibility. 


122  CULVERTS  AND  BRIDGES 

For  larger  bridges  the  services  of  a  competent  bridge  engi- 
neer should  be  secured. 

Fords. — Where  streams,  irrigation  canals,  or  other  water 
channels  are  shallow,  or  only  occasionally  carry  water,  the 
bridge  is  sometimes  omitted  and  the  crossing  made  by  wading. 
This  requires  a  hard  bottom  such  as  gravel  or  sand.  Where 
the  bottom  is  muddy,  as  in  some  of  the  Western  States,  the 
roadway  has  been  paved  with  concrete.  The  slab  of  concrete 


I 

Down  Stream  Side  Up  Stream  Side 

(o)  Cross  Section 


lb)  Longitudinal  Section 

c.&c 

FIG.  69. — Concrete  Ford. 

about  6  in.  thick  is  laid  directly  on  the  bottom  and  protected 
from  washing  beneath  by  sheet  piling,  or  by  extending  the 
concrete  downward,  a  foot  or  so,  on  the  sides,  Fig.  69.  In 
other  .cases  planks  lashed  together  with  wires  have  been  an- 
chored so  that  under  a  light  load  they  will  float  on  the  water, 
thus  allowing  a  foot  passenger  or  a  small  animal  to  cross  with- 
out wetting  the  feet,  and  under  a  heavy  load  sink  to  the  bottom, 
forming  a  solid  and  secure  roadway.  Fords  are  now  frequently 
used  in  parks  to  create  variety  in  the  road  scenery. 


CHAPTER  VI 
EARTH  ROADS 

IT  has  already  been  stated  that  a  large  percentage  of  all 
our  roads  are  of  the  type  known  as  earth  roads.  And  since  this 
must  perforce  remain  so  for  many,  many  years  it  is  well  to  study 
the  construction  and  maintenance  of  such  roads.  "  Earth," 
the  natural  soil,  consists  of  a  mixture  of  clay,  sand,  and  organic 
matter.  It  absorbs  water  readily  and  when  moistened  has  little 
power  to  withstand  pressure,  but  when  drained  to  the  proper 
consistency,  will  bear  loads  of  1  to  4  tons  per  square  foot  of  sur- 
face area  without  very  great  depression. 

The  kinds  of  "  earth "  vary  from  almost  pure  clay  to 
pure  sand.  But  for  the  purposes  of  classification,  roads  which 
are  practically  all  clay  or  all  sand  are  spoken  of  as  clay  or 
sand  roads  respectively.  And  those  composed  of  loam,  which  is 
a  mixture  of  these  elements  with  organic  matter,  as  earth  roads. 

Clay  is  decomposed  and  hydrated  rock.  The  particles  are 
extremely  small  and  have  great  affinity  for  water.  When 
moistened  to  just  the  right  consistency,  clay  is  almost  perfectly 
plastic,1  with  less  water  it  becomes  sticky,  stiff  and  finally 
loses  its  plasticity,  becomes  brittle,  easily  breaking  up  into  a 
fine  dust.  By  increasing  the  water  the  particles  move  freely, 
upon  each  other,  as  though  lubricated,  having  little  or  no  power 
to  withstand  an  applied  force. 

Sand  is  a  water  worn  detritus  finer  than,  although  similar 

to  gravel.     The  main  difference  between  sand  and  gravel  is 

one  of  size  of  particles.     While  clay  comes  largely  from  those 

rocks  which  in  the  breaking  down  processes  of  nature  change 

their  chemical  composition,  sand  is  usually  a  more  or  less  finely 

1  Flint  clays  do  not  have  the  property  of  plasticity. 

123 


124  EARTH  ROADS 

divided  rock  which  has  not  changed  its  chemical  composition. 
Granites,  gneisses,  and  other  feldspathic  varieties  are  the  princi- 
pal clay-forming  rocks,  while  quartz  bears  the  same  relation  to 
sand.  Though  the  particles  of  sand  have  an  affinity  for  water, 
they  are  also  so  much  thicker  than  the  film  of  water  which 
covers  them,  that  there  is  no  slipping  or  flowing  as  with  clay 
whose  particles  are  much  smaller  than  the  thickness  of  the  water 
film.  A  little  water  tends  to  bind  particles  of  sand  together. 
A  committee  of  the  American  Society  for  Testing  Materials 
has  proposed  the  following  definitions: 

Clay, — Finely  divided  earth,  generally  silicious  and  albuminous  which 
will  pass  a  200-mesh  sieve. 

Loam. — Finely  divided  earthy  material  containing  a  considerable 
proportion  of  organic  matter. 

Sand. — Finely  divided  rock  detritus,  the  particles  of  which  will  pass  a 
10-mesh  sieve  and  be  retained  on  a  200-mesh  sieve. 

Silt. — Naturally  deposited  fine,  earthy  material,  which  will  pass  a  200- 
mesh  sieve. 

Gravel. — Small  stones  or  pebbles  which  will  not  pass  a  10-mesh  sieve. 
The  differentiation  between  gravel,  sand,  silt  and  clay  should  be  made  on 
the  following  basis : 

Sizes  of  Particles.  Name. 

Retained  on  a  10-mesh  sieve Gravel 

Passing  a  10-mesh  and  held  on  a  200-mesh  sieve. .  .  .  Sand 

Passing  a  200-mesh  sieve Silt  or  Clay 

Drainage. — Just  what  effect  the  organic  matter  and  other 
impurities  may  have  on  the  road-making  qualities  of  the  soil 
is  riot  known.  Some  of  them,  no  doubt,  unite  with  the  clay  to 
form  a  slippery  soapy  mixture  which  prevents  good  bonding, 
others  assist  in  the  formation  of  a  hardened  surface.  There  is 
need  of  more  study  along  these  lines.  But,  according  to  present 
knowledge,  the  chief  element  which  affects  an  earth  road  is 
water.  With  too  much  water,  the  road  is  soft  and  unable  to 
bear  up  even  a  light  load,  "  tracks  "  easily,  then  dries  rough; 
with  too  little  water,  the  soil  on  top  pulverizes  into  a  powdery 
dust  under  the  action  of  the  wheels,  blows  away  leaving  the  road 
uneven  or  "  choppy";  with  just  the  right  amount  of  water  the 
road  is  reasonably  hard,  remains  smooth,  is  dustless  and  com- 


WIDTH   OF  RIGHT  OF  WAY  125 

fortable  to  travel.  Water,  therefore,  can  be  at  once  the  enemy 
and  the  friend  of  the  road.  It  is  better  to  have  too  little  than 
too  much  water.  The  general  principles  of  drainage  enunciated 
in  Chapter  IV  apply  with  especial  forcefulness  to  earth  roads, 
and  should  at  this  time  be  reviewed  carefully.  It  makes  no 
difference  whether  in  a  valley  or  on  a  hill,  an  undrained  earth 
road  is  always  a  poor  road. 

Alignment  and  Grades. — In  laying  out  earth  roads  care 
should  be  taken  to  place  them  in  the  best  location.  While  the 
effect  of  grades  is  not  so  noticeable  on  an  earth  road  as  upon  a 
hard,  smooth-surfaced  road  it,  nevertheless,  is  noticeable  and 
rise  and  fall  should  be  avoided  as  much  as  good  judgment  will 
warrant.  A  road  should  always  be  built  for  the  future  as  well  as 
the  present.  A  little  extra  work  may  remedy  a  bad  place  in  the 
road  which,  if  allowed  to  remain,  would  be  a  source  of  incon- 
venience and  expense  indefinitely. 

Width. — The  right  of  way  in  the  Prairie  States  is  usually 
4  rods  or  66  feet.  There  are,  of  course,  many  places  where  this 
amount  is  not  needed.  Likewise,  there  are  many  other  places 
where  it  is  all  needed.  Then  it  is  never  certain  what  demands 
the  future  may  make.  Many  valuable  pieces  of  public  property 
have  been  given  away  only  to  be  bought  back  at  high  prices 
subsequently.  If  the  right  of  way  is  not  needed  and  can  be 
farmed  by  adjacent  farmers  to  advantage,  let  the  public  officials 
lease  definite  portions  of  the  land  to  the  farmers  at  nominal 
rental  prices  but  not  give  up  the  right  to  its  future  use  should  it 
be  needed.  Where  farmers  have  been  allowed  to  plant  and 
crop  the  right  of  way  without  a  definite  contract  there  is  a  ten- 
dency to  encroach  too  much,  leaving  the  traveled  roadway  too 
narrow.  In  some  localities,  actions  in  court  have  been  neces- 
sary to  regain  such  ground,  the  owners  of  adjacent  land  claiming 
the  roadway  by  right  of  adverse  possession. 

Any  road  having  moderate  travel  should  have  at  least 
50  feet  right  of  way;  main  roads  having  considerable  travel  as 
much  as  the  traffic  justifies  even  100  or  more  feet.  "  In  the 
Middle  Atlantic  States,  the  regulation  width  is  49J  feet  for 
important  roads  and  33  feet  for  secondary  roads.  In  recent 


126  EARTH  ROADS 

years  there  is  a  tendency  to  increase  the  width,  a  minimum  of 
60  feet  being  preferred."  l 

According  to  the  authority  just  quoted,  Massachusetts' 
State-aid  roads  have  a  minimum  of  50  feet,  where  there  is  no 
likelihood  of  an  electric  traction  line,  and  with  a  trolley  line  60 
feet.  Texas  divided  its  roads  into  three  classes  having  widths 
of  60,  30,  and  20  feet.  Nearly  all  Mississippi  Valley  States  have 
either  60  or  66  feet.  A  few  Western  States  have  a  right  of  way 
of  100  to  165  feet.  In  New  Jersey  the  narrowest  State-aid  roads 
are  33  feet.  In  France  roads  are  divided  into  four  classes:  Na- 
tional, 66  feet  wide,  the  surface  improved  not  less  than  22  feet; 
departmental,  40  feet  wide,  improved  surface,  20  feet;  pro- 
vincial, 33  feet  wide,  improved  surface  20  feet;  neighborhood 
roads,  26  feet  wide,  improved  surface  16  feet.  Main  roads  in 
England  are  66  feet  wide,  improved  surface  22  to  30  feet.  On 
the  whole  66  feet  seems  an  admirable  width.  A  road  66  feet 
wide  contains  8  acres  per  mile  of  5280  feet. 

Clearing. — If  brush  or  trees  are  upon  the  right  of  way,  they 
must  be  cleared  off  and  the  roots  grubbed  out.  The  entire 
right  of  way  is  generally  cleared  and,  if  done  by  contract,  at  a 
certain  fixed  price  per  acre;  $30  to  $50  are  average  prices.  Sev- 
eral lands  of  stump  pullers  are  on  the  market,  but  blasting  is 
probably  as  cheap  as  any  method  of  removing  stumps.  Small 
stumps  and  brush  roots  are  removed  by  hand  labor.  Grubbing 
is  usually  paid  for  by  the  square  of  100  square  feet.  For  remov- 
ing hedges  or  rows  of  trees  along  the  road,  the  contractor  is  paid 
a  specified  price  per  rod.  Stumps  and  roots  need  not  be 
removed  under  fills,  but  trunks  or  branches  of  trees,  brush  or 
other  debris  should  never  be  used  in  them. 

Staking  Out. — The  staking  out  of  a  road  varies  greatly 
with  the  road.  Some  may  require  all  that  has  been  given  in 
Chapter  II.  The  minimum  number  will  probably  be  two  lines 
of  temporary  stakes  set  at  each  edge  of  the  roadway  to  be  graded. 
Others  such  as  center  line,  slope  stakes,  bridge  openings,  ref- 
erence stakes  and  so  on  may  be  added  as  required.  The  trav- 
eled roadway  should,  unless  there  are  very  good  reasons  for 
1  George  D.  Steel  in  "Better  Roads  and  Streets,"  March,  1914. 


WIDTH  OF  ROADWAY 


127 


changing,  be  staked  out  in  the  middle  of  the  right  of  way.  Care 
in  this,  having  the  edges  straight,  and  other  minor  details  add 
greatly  to  the  attractiveness  of  the  highway. 

Width  and  Cross-section  of  Roadway. — The  width  across  the 
ordinary  road  vehicle  from  center  to  center  of  tire,  or  gauge  of 
the  vehicle,  in  the  Northern  and  Western  States  is  4  feet  8 
inches;  the  width  over  all  varies  from  5J  to  7  feet.  Vans, 
trucks  and  loaded  hay-racks  are  from  7  to  10  feet  wide.  In  a 
few  of  the  Southern  States  a  gauge  of  5  feet  is  still  in  use.  The 
maximum  width  and  commonly  traveled  width  of  roadways 
measured  in  Massachusetts  and  printed  in  the  report  of  the 
Massachusetts  Highway  Commission  for  1900  is  shown  in 
tabular  form  below: 


Width  of  road  in  feet  

7 

8 

9 

10 

11 

12 

13 

Number   of  roads  found  with   above 

traveled  width  as  maximum  

2 

6 

2 

28 

"8 

Number  of  roads  found  with  above 

traveled  width  commonly  used  

12 

17 

25 

32 

10 

30 

3 

Width  of  road  in  feet 

14 

15 

16 

17 

18 

19 

20 

Number  of  roads  found  with  above 

traveled  width  as  minimum  

23 

30 

8 

1 

23 

1 

10 

Number  of  roads  found  with  above 

traveled  width  commonly  used  

8 

13 

2 

0 

4 

0 

2 

Width  of  road  in  feet  

21 

22 

23 

24 

25 

26 

33 

Number   of  roads  found  with  above 

traveled  width  as  maximum  

10 

1 

.0 

2 

4 

1 

1 

Number   of  roads  found  with   above 

traveled  width  commonly  used  

0 

1 

0 

0 

1 

0 

00 

Harger  and  Bonney  1  measured  New  York  State  improved 
roads  and  found  heavy  traffic  checked  well  with  the  Massa- 

1  Highway  Engineers'  Handbook,  p.  19. 


128 


EARTH   ROADS 


chusetts  results  but  that  the  maximum  widths  were  greater, 
averaging  from  18  to  21  feet;  this  they  explained  as  due  to 
increase  of  automobile  traffic  since  the  Massachusetts  measure- 
ments were  made  1896-1900. 

From  the  above  it  would  seem  that  7  feet  is  the  minimum 
allowable  width.  If  this  could  be  increased  a  foot  on  each  side 
the  traffic  would  not  be  confined  to  such  narrow  trackway  and 
rutting  would  be  greatly  diminished.  Where  two  lines  of 
vehicular  traffic  is  required,  16  feet  should  be  the  minimum, 
but  for  safety  and  ease  of  passing  while  traveling  at  some  speed, 
20  feet  will  be  better.  If  the  number  of  lines  (lanes)  of  traffic 


...Si..  J«— »'-..^« 17- 

(a)  Village  Street 


U Not  less  than  30 

l^-.g-'-X^ 20-= >k--5-- 


Koad  Machine  Work  on  Light  Soils 


FIG.  70.  FIG.  72. 

Typical  Cross-sections. 

it  is  desired  safely  to  pass  abreast  be  represented  by  n,  the 
width  in  feet  may  be  taken  as 

w=lQn. 

Figs.  70,  71,  and  72  show  some  standard  cross-sections  of 
earth  roads  as  adopted  by  engineers  and  state  highway  com- 
missions. 

The  following  values  for  an  earth  road  cross-section,  Fig.  73, 
are  suggestive: 


SUGGESTED    DIMENSIONS    FOR    EARTH    ROADS     129 


A  =  width  of  traveled  road  =  10n  feet; 

n  =  integer,  1,  2,  3,  4,  5,  6;  depending  on  traffic  (lanes); 

B  =  3%Vn  feet  (in  cuts  or  on  high  fills  may  be  reduced!); 

C  =  4n  inches; 

D  =  2B  inches; 

d  =  approximately  T$A',  for  level  cross-sections. 


FIG.  73. — Typical  Cross-section  for  Earth  Road. 

E  =  Width  from  bottom  of  ditch  to  bottom  of  ditch. 

A  =  Width  of  Traveled  Road  =10«. 

n  =Interger  1,  2,  3,  4,  etc.,  depending  on  traffic. 

B  =  Width  of  Gutter  =3j  V«,  ft.     In  cuts  or  on  high  fill  may  be  reduced  one-half. 

C  =Crown  height  =4n  inches. 

D  =  Gutter  depth  =2B  inches. 

d  -  Approximately  j^A  for  level  cross-sections. 

DIMENSIONS 


A 

B 

C 

D 

E 

n 

Feet 

Feet 

Inch 

Inch 

Feet 

1 

10 

3.5 

4 

5 

17 

2 

20 

5 

8 

10 

30 

3 

30 

6 

12 

12 

42 

4 

40 

7 

16 

14 

54 

5 

50 

7.75 

20 

16 

66 

6 

60 

8.5 

24 

17 

77 

On  a  fill  less  than  4  feet  high  the  slope  of  the  bank  may  be, 
1  :  3,  for  greater  fills  1  :  1J  with  guard  rails  placed  along  the 
shoulder.  In  cuts  slopes  will  depend  on  the  character  of  the 
soil;  for  ordinary  earth  and  clay  1  :  1  has  proven  sufficient.  In 


130  EARTH  ROADS 

a  cut  the  depth  of  the  gutter  may  be  reduced  to  one-half  the 
dimensions  given  in  the  table  in  order  to  lessen  cost  of  excava- 
tion. On  grades  greater  than  3  per  cent,  the  slope  of  the  crown 
may  be  increased  slightly,  and  the  bottom  of  the  gutter  paved 
with  concrete,  cobbles,  broken  stone,  or  brick.  The  width  of  a 
road  should  always  be  as  narrow  as  the  traffic  will  allow  in 
order  that  the  cost  of  construction  and  maintenance  may  be 
kept  down.  Few  country  roads,  except  near  market  centers, 
need  to  have  a  traveled  way  of  more  than  20  feet,  or  30  feet 
from  bottom  of  ditch  to  bottom  of  ditch. 

GRADING 

The  reduction  of  a  roadway  to  conform  to  the  grade  (gra- 
dient) and  cross-section  suitable  for  use  is  called  grading.     In 


FIG.  74.— A  Reversible  Road  Grader. 

grading,  the  surplus  earth  in  those  places  above  grade  is  cut 
away  and  filled  into  those  places  below  grade.  Frequently  the 
grade  is  established  upon  an  embankment  for  purposes  of 
drainage;  the  earth  for  the  embankment  may  be  brought  in 
from  the  sides  of  the  road,  that  is.  borrowed;  the  places  from 
which  it  is  taken  are  borrow  pits.  Sometimes  it  is  better 
to  waste  the  earth  from  a  cut  along  the  roadway  rather  than 
haul  it  a  long  distance  to  a  fill. 

Grading  Machines  arid  Tools  and  Methods  of  Using  Them.— 
Blade  Grader. — The  blade  or  scraping  grader,  Fig.  74,  has  proven 
itself  to  be  a  most  efficient  road  making  machine.  By  pulling 


BLADE   GRADER 


131 


a  moderately  heavy  grader  with  a  traction  engine  ordinary 
roads  are  being  made  in  the  Middle  Western  States  at  a  cost 
of  $50  to  $100  per  mile.  There  are  many  forms  of  this  machine 


Plowing  the  Ditch 


Pushing  Earth  Jowardthe  Centsr 


Cutting  the  Outside  Slope  of  the  Ditch 


Pushing  Earth  Toward  and  Grading  the  Centsr 


Original  Ground  Surface 

FIG.  75. — Diagrams  Showing  the  Use  of  the  Road  Machine. 

but  all  consist  essentially  of  a  slightly  curved  blade  attached 
to  a  stout  frame  on  wheels.    The  blade  is  usually  made  up  of 


FIG.  76. — A   Good   Example   of   Grading  Operations   in   Grant   Parish, 

Louisiana. 

two  parts,  a  mold-board  and  a  lay  or  cutting  edge.     It  is  adjust  • 
able  to  almost  any  position  with  either  end  forward  and  will 


132 


EARTH  ROADS 


throw  the  dirt  as  desired  to  right  or  left;  it  can  be  raised  or 
lowered  and  set  at  various  angles.  It  will  also  plow  a  furrow, 
push  earth  sideways,  and  level  and  smooth  the  surface.  By 
shifting  the  wheels  laterally  or  by  tilting  them  on  their  axles, 
side  thrust  is  taken  care  of. 

The  diagrams,  Fig.  75,  and  Figs.  76  and  77,  show  the  method 
of  using  the  grader.  The  first  round  plows  a  furrow,  succeeding 
rounds  deepen  and  widen  it,  at  the  same  time  the  loosened  earth 


FIG.  77.— Trimming  Off  the  Side  with  a  Road  Grader  on  a  State-aid 
Project  in  Nebraska. 

is  pushed  toward  the  center  of  the  road.  In  making  the  fill 
the  earth  is  allowed  to  sift  out  beneath  the  blade  as  it  is  being 
pushed  toward  the  center.  It  is  better  not  to  attempt  to  push 
too  much  earth  at  once,  for  if  the  center  is  not  quite  high  enough 
a  little  more  earth  can  be  pared  from  the  side  ditch  and  moved 
over.  If  too  full,  on  the  other  hand,  the  blade  must  be  straight- 
ened across  the  roadway  and  the  extra  earth  distributed  over 
the  graded  way. 

Harrow. — A  tooth  harrow  such  as  is  used  on  farms  or  the 
A-shaped  harrow  described  in  the  chapter  on  gravel  roads  is 


HARROW,  PLOW 


133 


useful  for  smoothing.     It  also  assists  the  settling.     Disk  har- 
rows, Fig.  78,  may  be  used  similarly. 

Plow. — The  common  plow,  Fig.  79,  is  indispensable.     In 
fact,  even  when  blade  grader  work  is  being  done  the  plow  is 


FIG.  78. — Double  Disc  Harrow,  Useful    in  Working*  Earth  Roads  Pre- 
paratory to  Smoothing. 

useful  to  open  the  outlining  furrow  or  for  loosening  earth  that 
is  too  compact  for  the  grader.  While  an  ordinary  field  plow 
may  be  used  heavier  types  are  especially  constructed  for  road 
work.  Some  turn  the  soil  to  the  right  others  to  the  left;  to 
the  beam  is  attached  a  gauge  wheel  or  shoe  to  control  the 


FIG.  79.— Road  Plow. 

depth;  large  plows  are  supplied  with  a  cutter  (coulter),  rolling 
or  stationary,  to  assist  in  separating  the  sod.  Four  or  more 
horses  may  be  used  to  advantage.  With  a  driver  and  laborer 
to  hold  the  plow  about  400  cubic  yards  of  loam  may  be  loosened 
in  a  day  of  eight  hours;  in  gravelly  loam  about  300  cubic  yards; 
and  in  stiff  clay  or  heavy  sod,  200  cubic  yards. 


134 


EARTH  ROADS 


Drag  or  Slip  Scraper. — This  is  a  scoop  or  bowl,  Fig.  80,  to 
which  is  attached  a  bail  by  which  it  is  drawn  along.  The  front 
edge  of  the  scoop  is  a  sharpened  plate  while  at  the  rear  is 
attached  a  pair  of  handles.  The  ends  of  the  bail  are  pivoted  to 


No.  1.    Capacity  7  cu.  ft. 

Actual  We.  97  Ibs 
No.  2.  Capacity  5  cu  ft. 

Actual  Wt.  84  Ibs. 

No.  J      Capacity  3  cu  ft. 

*  Actual  Wt  74  Ibs 


FIG.  80.— Drag  Scraper. 

the  scoop  in  such  a  manner  that  when  the  handles  are  slightly 
lifted  the  cutting  edge  is  brought  into  the  loosened  soil  and  the 
scoop  filled;  when  the  handles  are  lowered  the  edge  just  clears 
the  ground  and  the  scoop  slides  along  on  its  bottom;  by  raising 
the  handles  a  little  higher  than  necessary  to  fill  the  scoop  the 


FIG.  81. — Tongue  Scraper. 

cutting  edge  catches  in  the  ground  and  the  scraper  is  dumped 
by  the  pull  of  the  horses.  In  using  the  scraper  ordinarily  a 
stretch  6  or  8  feet  wide  and  100  or  200  feet  long  is  plowed  parallel 
to  the  roadway,  preferably  in  a  direction  which  will  throw  the 
earth  toward  the  road's  center.  The  teams  drawing  the  scrapers 


SCRAPERS 


135 


are  driven  in  a  more  or  less  elliptical  course,  the  loosened  earth 
being  taken  from  the  plowed  land  in  such  a  manner  that  the 
horses  will  step  on  as  little  of  it  as  possible,  and  dumped  with  the 
piles  closely  adjoining  each  other,  making  a  comparatively 
smooth  surface.  The  operator  may  help  to  smooth  the  surface 
by  holding  the  scraper  handles  and  not  allow  it  to  dump  its 


No.  1. 
No.  2. 
No.  3. 


FIG.  82. — Fresno  or  Buck  Scraper. 

Made  in  Three  Sizes. 

5    feet  wide.  Weight  360  pounds.  For  three  or  four  horses. 

4    feet  wide.  Weight  300  pounds.  For  two  or  three  horses 

3£  feet  wide.  Weight  260  pounds.  For  two  horses. 

The  Nos.  1  and  2  are  most  popular  for  road  work. 


entire  load  in  one  spot.     The  capacity  of  scrapers  vary  from  3 
to  13  cubic  feet,  5  to  7  being  common. 

Tongue  or  Pole  Scraper. — This  consists  of  a  wooden  box, 
Fig.  81,  to  which  handles  are  attached  and  has  a  tongue  as  its 
name  indicates.  The  cutting  edge  is  a  steel  blade  which  can 
be  taken  off  to  sharpen  or  replace.  The  under  side  of  the  box 
is  equipped  with  steel  shoes  upon  which  it  slides.  This  scraper 
is  useful  for  leveling  up  as  the  blade  is  straight  and  can  be  held 
at  any  angle  by  means  of  a  chain,  thus  depositing  the  earth  in 


136 


EARTH   ROADS 


layers  from  1  to  10  inches  thick.     It  is  also  suitable  for  filling 
tile  ditches. 

Fresno  or  Buck  Scraper. — This  scraper,  Fig.  82,  is  about 
twice  the  width  of  the  ordinary  drag  scraper,  considerably 
deeper,  and  has  a  capacity  of  12  to  18  cubic  feet.  It  has  one 
handle  only  and  that  at  the  center.  The  shoes  are  bent  around 

the  front  of  the  scoop  and  answer 
for  skids  both  when  it  is  right  side 
up  and  full  and  when  tipped  up 
and  empty.  The  Fresno  is  es- 
pecially useful  for  "  bucking  " 
light  loamy  earth  from  the  side 
ditches  into  the  fill.  In  such 
cases  often  a  cubic  yard,  or  even 
a  yard  arid  one-half,  can  be 
brought  in,  that  is,  pushed  in  at 
one-time;  much  more  than  the 
volume  of  the  scoop  alone.  Extra 
large  fresnos  are  now  made  to  be 
drawn  by  tractors. 

Wheel  Scrapers. — The  scoop 
of  the  scraper,  Fig.  83-,  is  mounted 
on  two  wheels  with  a  bent  shaft 
for  the  axle;  it  is  equipped  with 
levers  for  lowering,  filling,  raising, 
and  dumping.  It  has  a  tongue 
and  is  drawn  by  two  horses. 
Wheel  scrapers  are  especially  use- 
ful where  earth  is  to  be  carried 
a  considerable  distance  before 
Some  makes  have  front  end-gates  which,  by  pre- 
venting the  earth  from  sliding  out  in  front,  increase  the 
carrying  capacity. 

The  ground  should  be  thoroughly  plowed.  The  operator 
drops  the  scoop  by  means  of  a  lever  and  holds  the  lever  upright 
or  a  little  forward  which  brings  the  cutting  edge  of  the  scraper 
into  the  soil.  When  the  scoop  is  filled,  without  stopping  the 


FIG.  83.— Wheel  Scraper, 
dumping. 


DUMP   WAGONS  137 

horses,  the  operator  draws  the  lever  back  and  latches  it  thus 
lifting  the  scoop  from  the  ground  where  it  swings  easily  while 
riding  to  the  dump.  By  again  raising  the  lever  and  pushing  it 
forward  the  cutting  edge  of  the  scraper  catches  into  the  ground 
and  the  forward  motion  of  the  team  completes  the  dumping. 
The  smaller  wheel  scrapers,  except  in  very  hard  material,  require 
but  one  man  to  operate  them.  The  larger  sizes  require  an  extra 
man  to  assist  with  the  loading.  A  "  snatch  "  team  can  be  used 
advantageously  in  loading.  Four-wheel  scrapers  are  also  in  use. 
Dump  Wagons. — A  number  of  different  kinds  of  dump 
wagons  are  on  the  market,  most  of  them  having  hinged  bottoms 
which  can  be  locked  into  place  by  chains  and  levers  and  released 
when  the  load  is  to  be  dumped,  Fig.  84.  In  a  few  wagons  and 


FIG.  84. — Dump  Wagon. 

many  tracks  the  whole  bed  is  tipped  up  by  means  of  a  hoist 
and  the  load  slipped  out  the  rear  end.  It  is  claimed  the  latter 
will  spread  the 'earth  in  uniform  layers  of  any  required  thickness 
up  to  1  foot.  The  wagons  are  filled  either  by  men  with  hand 
shovels,  by  a  steam  shovel,  or  with  an  elevating  grader.  When 
cuts  and  fills  are  heavy  and  distances  of  haul  great  they  are  very 
efficient.  Two  horses  are  used  on  each  wagon;  the  driver  does 
the  dumping.  The  tires  are  made  at  least  4  inches  broad  in 
order  that  they  may  not  sink  much  into  the  soft  earth. 

Dump  Boards. — Dump  boards  are  made  of  planks  2  inches 
thick  and  from  4  to  6  inches  wide  and  about  10  feet  long?  They 
are  used  with  an  ordinary  wagon.  The  bed  is  removed,  a  pair 
of  side-boards  about  12  inches  wide  placed  against  the  standards 
and  the  several  dump  boards  fitted  between,  these  lying  loosely 


138 


EARTH  ROADS 


upon  the  bolsters  form  the  bottom  of  the  box  into  which  the 
earth  is  thrown.  By  turning  the  bottom  boards  up  edgewise, 
first  removing  one  side-board,  the  load  is  dumped  through  the 
running  gears  of  the  wagon.  Dump  boards  are  not  as  efficient 


IG.  85. — Dump  Truck  Fitted  with  Kilbourne  &  Jacobs  Hoist. 

as  the  dump  wagon,  but  farm  wagons  can  easily  be  transformed 
into  dump-board  wagons  at  small  cost  for  temporary  use. 

Elevating  Grader. — The  elevating  grader,  Fig.  86,  consists  of 
a  heavy  plow  and  an  elevator  mounted  upon  four  wheels.     The 


FTG.  86.— Russell  Elevating  Grader. 

plow  tufns  the  earth  upon  a  conveying  belt  which  carries  it  up 
and  to  one  side  of  the  machine.  At  the  top  of  the  elevator  the 
belt  turns  over  a  pulley  and  dumps  the  earth  into  a  chute  down 
which  it  runs  to  a  wagon  driven  along  side  the  grader,  or  directly 


VARIOUS  TOOLS  139 

upon  the  ground  near  the  middle  of  the  roadway.  The  grader  is 
generally  drawn  by  a  tractor  but  sometimes  ten  or  twelve  horses 
are  used. 

Spades  and  Shovels. — Spades  are  used  for  ditching  and  dig- 
ging. The  shovel  is  used  for  moving  earth  as  it  has  a  larger 
bowl  than  the  spade.  Some  road  men  prefer  the  pointed  shovel; 
it  cuts  better  and  can  be  used  for  digging.  The  square- 
edged  shovel  is  better  for  mixing  concretes,  for  cleaning  a  smooth 
surface  or  for  leveling  off  earthwork.  D-handles  and  long 
straight  handles  are  both  used.  Scoop  shovels  having  deep 
bowls  especially  designed  for  shoveling  grain  are  valuable 
where  a  light  material  such  as  snow  is  to  be  removed. 

Picks  are  usually  two-pointed  and  are  used  for  loosening 
the  soil  before  the  shovels.  In  stony  soil  they  soon  wear  off 
and  have  to  be  repointed  by  a  blacksmith.  A  matlock  is  a  form 
of  pick  with  one  point  replaced  by  a  chopping  ax-like  edge  and 
the  other  by  an  adz-like  edge.  They  are  serviceable  for  grub- 
bing. 

Axes  and  Brush  Hooks  are  necessary  where  clearing  is  re- 
quired. 

A  Corn  Knife  is  valuable  for  cutting  high  weeds  as  well 
as  corn  stalks. 

A  Scythe  and  a  Horse-drawn  Mower  are  often  useful  to 
remove  grass.  Rakes  and  hoes  also  have  their  place  in  road  work. 

Steam  Shovels,  Drag  Line  Scrapers  and  Industrial  Railways 
are  all  in  use  for  heavy  work.  Steam  shovels  mounted  on  broad- 
tired  trucks  will  excavate  earth  rapidly  -and  deposit  it  either  on 
the  fill  being  made,  to  one  side  of  the  cut,  or  in  wagons  to  be 
hauled  to  place  of  disposal.  Drag-line  scrapers  and  derricks 
with  excavating  buckets  are  used  in  a  similar  manner.  Indus- 
trial railways  are  made  of  light  rails  joined  together  in  sections 
for  easy  handling,  spaced  about  2|  to  3  feet  apart,  with  portable 
switches,  turnouts,  and  turntables.  Trains  of  small  dump  cars 
operated  by  steam,  gasoline  or  electric  locomotives  are  pushed 
along  the  track  which  is  laid  along  or  parallel  to  the  roadway 
being  built.  They  are  filled  with  a  steam  shovel  or  clam-shell 
bucket,  or  possibly  by  hand,  and  hauled  to  the  point  of  emptying. 


140  EARTH  ROADS 

As  the  cut  or  the  embankment  is  widened  the  track  is  shifted 
sideways.  These  can  be  used  only  where  the  magnitude  of  the 
operation  is  such  as  to  warrant  the  high  first  cost.  Embank- 
ments constructed  by  industrial  railway,  since  they  are  not 
walked  upon  by  the  horses  and  men,  shrink  more  than  those 
built  by  scraper.  Also  additional  help  may  be  required  to  dis- 
tribute the  earth  in  the  fill. 

Borrowed  Earth  and  Borrow  Pits. — Usually  sufficient  mate- 
rial for  the  embankments  may  be  obtained  from  the  side  ditches 
and  the  excavations  as  staked  out  by  the  engineer.  Sometimes, 
however,  earth  must  be  "  borrowed."  Borrow  pits  should  be 
made  of  regular  shape  in  order  that  they  may  be  easily  measured. 
Also,  they  should  drain. completely;  water  collecting  in  borrow 
pits  often  soaks  under  the  road  and  softens  the  subsoil,  destroy- 
ing the  stability  of  the  road.  A  berm  of  at  least  3  feet  should  be 
left  between  the  toe  of  the  slope  and  the  borrow  pit. 

Embankment. — The  embankment  should,  preferably,  be 
carried  up  in  horizontal  layers,  each  carried  out  to  its  proper 
width.  While  it  is  usually  stated  that  organic  matter  should 
not  be  allowed  in  an  embankment  it  will  probably  do  no  harm 
to  allow  sod  to  be  placed  in  such  providing  it  is  covered  to  a 
depth  of  1  or  more  feet  or  is  thoroughly  harrowed  or  disked  to 
break  it  up. 

Haul  and  Overhaul. — The  contractor  is  usually  paid  for 
either  excavation  or  fill  but  not  for  both.  Transporting  the 
material  a  specified  distance,  say  500  feet,  is  generally  included 
in  the  contract  price.  The  average  length  of  haul  is  deter- 
mined by  locating  the  center  of  gravity  of  the  cut  and  the  center 
of  gravity  of  the  fill.  If  the  center  of  gravity  of  the  cut  is  more 
than  the  specified  distance  (500  feet)  from  the  center  of  gravity 
of  the  corresponding  fill,  overhaul  is  allowed  for  the  entire 
amount  of  material  in  the  cut  for  the  distance  between  the  cen- 
ters of  gravity  in  excess  of  the  free  haul  distance. 

Shrinkage. — It  should  be  remembered  that  earth  fills  will 
shrink  from  10  to  15  per  cent  and  due  allowance  should  be  made, 
say  for  depth  6f  fill  up  to,  8  feet,  10  per  cent;  8  to  12  feet,  12 
per  cent;  12  to  18  feet,  15  per  cent. 


EARTH   ROAD  MAINTENANCE 


141 


Tractors  vs.  Horses. — There  is  no  doubt  that  it  is  cheaper 
to  construct  earth  roads  by  using  a  tractor  to  pull  the  grader 
than  to  use  horses.  A  larger  grader  may  be  used ;  more  earth  is 
moved  at  one  time,  and  because  of  the  larger  machine  there  is  less 
jumping,  and  the  operation  is  smoother  and  easier.  Many 
counties  buy  the  machines  and  keep  the  same  outfit  of  men 
working  on  them  all  summer;  the  men  become  adept  and  the 
cost  of  building  is  correspondingly  decreased.  In  the  Prairie 
States,  roads  18  feet  wide  are  being  graded  at  $50  to  $100  per 
mile,  including  interest  on  the  cost  of  machinery. 

MAINTENANCE 

Two  systems  for  the  maintenance  of  earth  roads  might  be 
denominated  periodic  and  continuous.  The  old  scheme,  handed 


****««?        PLAN 


FIG.  87.— The  King  Split  Log  Drag.1 

1  From  "The  Use  of  the  Split  Log  Drag  on  Earth  Roads,"  by  D.  Ward  King,  Far- 
ieis'  Bulletin  321,  U.  S.  Department  of  Agriculture. 


142  EARTH   ROADS 

down  from  early  history,  of  summoning  free-holders  to  work  the 
roads  at  certain  seasons  of  the  year  represents  the  extreme 
periodic,  and  the  patrol  system,  whereby  a  man  spends  his 
entire  time  in  daily  looking  after  a  definite  portion  of  road,  the 
extreme  continuous.  No  one  now  will  uphold  the  extreme 
periodic  system;  on  the  other  hand  most  earth  roads  are  used 
too  little  to  warrant  the  use  of  the  patrol  system. 

Dragging. — The  simplest  and  best  method  of  maintaining 
an  earth  road  is  by  dragging.  For  years  race  tracks  have  been 
dragged  or  floated  for  the  purpose  of  keeping  the  surface  smooth 
and  reducing  the  tractive  resistance.  During  recent  years  this 
method  has  been  applied  to  the  ordinary  earth  road  and  the 


FIG.  88. — Plank  Drag. 

drag  most  generally  used  is  some  form  of  the  original  designed 
by  D.  Ward  King  of  Maitland,  Mo. 

Drags. — Mr.  King  made  his  drag  of  a  split  log,  Fig.  87,  but 
now  drags  are  constructed  also  of  planks  and  of  steel,  Figs. 
88  and  89. 

In  Farmers'  Bulletin  321,  U.  S.  Department  of  Agriculture, 
by  D.  Ward  King,  detailed  description,  method  of  construction 
and  use  are  given.  Fig.  87  shows  a  plan  of  the  drag  taken  from 
that  bulletin.  The  slabs  are  fastened  together  with  stakes 
wedged  into  2-inch  holes  and  a  brace  of  2X4  inch  material  is 
placed  diagonally  at  the  ditch  end  of  the  drag.  "  The  brace 
should  be  dropped  on  the  front  slab  so  that  its  lower  edge  shall 
lie  within  an  inch  of  the  ground  while  the  other  end  should  rest 
in  the  angle  between  the  slab  and  the  end  of  the  stake.  A  strip 
of  iron  3J  feet  long,  3  or  4  inches  wide  and  \  inch  thick  may  be 


DRAGS  AND   DRAGGING  143 

used  for  the  blade.  This  should  be  attached  to  the  front  slab, 
so  that  it  will  be  J  inch  below  the  lower  edge  of  the  slab  at  the 
ditch  end,  while  the  end  of  the  iron  toward  the  middle  of  the 
road  should  be  flush  with  the  edge  of  the  slab.  The  bolts 
holding  the  blade  in  place  should  have  flat  heads  and  the  holes 
to  receive  them  should  be  countersunk.  If  the  face  of  the  log 
stands  plumb  it  is  well  to  wedge  out  the  lower  edge  of  the  blade 
with  a  three-cornered  strip  of  wood  to  give  it  a  set  like  the  bit 
of  a  plane." 

A  cover  of  inch  boards  spaced  an  inch  apart  and  held  by 


FIG.  89.— Steel  Road  Drag. 

cleats  on  the  under  side  is  laid  over  the  stakes  to  furnish  a  plat- 
form for  the  driver  to  stand  upon. 

The  Theory  and  Use  of  the  Drag.1 — Dragging  if  properly 
done  not  only  shapes  and  crowns  the  road  by  carrying  a  small 
amount  of  earth  toward  the  center  at  each  dragging,  smoothing 
and  honing  the  same,  but  it  also  is  a  puddling  and  smearing 
process,  and  if  the  highest  success  is  to  be  obtained  these  last 
two  elements  must  enter. 

If  soil  taken  from  the  field  be  placed  in  a  sieve  and  water 
turned  upon  it,  on  account  of  the  granular  condition  of  the 
soil  the  water  soon  soaks  in  and  much  passes  clear  through  and 

Abstracted  from  an  article  on  "The  Use  of  the  King  Road  Drag," 
by  G.  R.  Chatburn  in  Huebinger's  Guide  Book  of  the  Omaha-Lincoln- 
Denver  Highway. 


144  EARTH  ROADS 

out  the  meshes  of  the  sieve.  But  if  the  water  and  soil  be  stirred 
and  mixed  to  form  sticky  mud  and  then  pressed  into  a  cup  shape 
in  the  sieve  it  will  be  found  to  hold  water,  that  is,  if  additional 
water  be  put  into  the  mud  cup  and  covered  by  a  glass  plate  to 
prevent  evaporation,  the  sieve  thus  smeared  inside  with  "  pud- 
dle "  will  retain  the  water  for  a  considerable  number  of  days. 
Thus  in  the  process  of  puddling,  the  air  is  worked  out,  the  par- 
ticles become  pressed  closely  together  and  the  voids  between 
them  filled  with  water;  a  sticky  or  gummy  colloidal  mass  is 
formed  which  is  impervious  to  the  passage  of  more  water,  and, 
such  water  as  is  needed  to  form  this  colloidal  state  is  tenaciously 
held  and  will  be  given  up  reluctantly  only  upon  the  application 
of  pressure  or  through  evaporation. 

The  water  hole  or  storage  reservoir  of  the  stockman,  the 
buffalo-wallow  of  the  plains  region,  the  ordinary  rnud  puddle 
of  the  hog  yard  or  the  roadway,  all  hold  water  because  lined  with 
puddle — colloidal  soil  made  dense  and  impervious  by  kneading. 
On  the  other  hand  if  the  contained  water  is  of  the  right  amount, 
such  soil  will  pack  under  pressure  or  by  tamping  until  if  spread 
upon  a  firm  foundation  it  is  capable  of  sustaining  a  considerable 
load  without  either  squashing  or  grinding  into  dust.  A  well-- 
crowned road  covered  with  puddle  in  its  ideal  condition  of 
dampness  has  a  water-tight  roof  and  all  it  needs  in  addition  is  a 
thorough  side  and  under  drainage  to  give  it  a  dry  cellar;  a  road, 
like  a  house,  should  have  a  tight  roof  and  a  dry  cellar. 

Dragging  a  road  immediately  after  a  rain,  while  the  ground 
is  still  wet,  but  not  too  sticky,  puddles  the  soil  and  smears  it 
over  the  top;  presses  out  the  surplus  water  and  leaves  the  sur- 
face smooth  and  hard  for  service;  and  when  the  next  rain  comes, 
the  water  rapidly  runs  off  before  it  has  had  time  to  soak  deeply  in. 
Another  dragging  puddles  and  smears  some  more;  the  drag 
having  been  set  to  bring  fresh  earth  from  the  side  toward  the 
center,  the  thickness  of  the  roof  gradually  increases  with  each 
dragging  until  in  time  there  are  from  2  to  6  inches  of  compact 
hard  crust.  The  wheel  tracks  being  obliterated,  the  entire 
surface  of  the  dragged  highway  receives  the  uniform  beating 
and  packing  of  hoofs  and  wheels;  the  formation  of  ruts,  the 


THEORY  AND  USE  OF  THE  ROAD  DRAG 


145 


worst  possible  thing  that  can  happen  to  any  road  surface  is 
avoided. 

Method  of  Using  the  Drag. — The  successful  use  of  the  drag 
requires  first  a  light  drag;  one  so  light  that  one  man  can  easily 
load  it  into  a  wagon,  but  still  stiff  and  rigid  enough  hot  to  hinder 
materially  its  use  on  the  road.  The  driver  should  ride  the 
drag,  not  seated  with  an  umbrella  over  him,  but  standing  so 
that  by  changing  his  position  he  can  make  it  dig  deeper  or  not 
so  deep  as  he  wishes.  To  make  it  dig  deeper,  throw  the  entire 
weight  on  one  foot  near  the 
cutting  or  forward  corner  of 
the  drag  at  A,  Fig.  90;  if 
less  deep  throw  the  weight 
back  upon  the  foot  B  or  step 
to  C.  If  the  front  rail  or  slab 
becomes  clogged  with  weeds, 
or  it  is  desired  to  drop  a 
quantity  of  earth  to  fill  a 
hole,  the  driver  should  step 
quickly  to  the  point  D,  then 
back  again  to  A.  The  earth 
dug  up  by  the  cutting  blade 
should  gradually  work  along 
and  sift  under  the  forward 
rail.  The  front  rail  may  be 
set  inclined  backward  so  that 
it  forms  a  plane-bit  cutting 
edge  while  the  rear  crushes  FIG;  go._Method  of  Using  the  Drag. 
and  plasters  down  the  earth 

which  has  sifted  under  the  forward  rail,  leaving  it  smooth  as 
butter  is  left  on  a  piece  of  bread  by  the  knife,  or  mortar  by  the 
trowel  of  the  workman.  Lengthening  the  hitch  will  also  cause 
the  drag  to  move  more  earth. 

It  is  impossible  to  state  the  exact  length  of  hitch,  the  best 
angle  to  draw  the  drag,  or  the  position  of  the  driver,  for  these 
will  all  vary  with  the  character  and  condition  of  the  soil,  the 
length  of  time  the  road  has  been  dragged,  and  the  condition  of 


146 


EARTH  ROADS 


the  roadbed  at  the  time  of  dragging.  The  driver,  if  a  man  of 
intelligence,  can  by  trial  soon  ascertain  these  things  for  himself. 
But  it  may  be  said  the  total  amount  of  fresh  earth  brought 
toward  the  center  should  usually  all  be  spread  and  crushed  by 
the  drag.  A  ridge  or  windrow  of  earth  should  never  be  left  in 
the  middle  of  the  road.  Care  in  digging  up  just  as  much  earth 
as  will  uniformly  sift  out  under  the  rail  of  the  drag  by  the  time 
the  top  of  the  road  is  reached,  will  avoid  this.  But  if  for  any 


FIG.  91.— A  Well-dragged  Earth  Road. 

cause  more  earth  than  sufficient  has  been  conveyed  to  the  cen- 
ter it  can  be  smoothed  by  using  the  drag  straight  instead  of 
diagonally  the  last  trip  over.  If  the  center  gets  too  high,  or 
higher  than  the  standard  cross-section  of  the  road,  Fig.  73,  the 
drag  should  be  inclined  in  the  opposite  direction  occasionally. 
Rules  for  Dragging. — The  Illinois  Highway  Commission 
distributed  to  its  road  overseers  the  following  rules  for  dragging, 
which  are  both  concise  and  explicit: 

Make  a  light  drag,  which  is  hauled  over  the  road  at  an  angle  so  that  a 
small  amount  of  earth  is  pushed  to  the  center  of  the  road. 
Drive  the  team  at  a  walk. 
Ride  on  the  drag;  do  not  walk. 
Begin  on  one  side  of  the  road,  returning  on  the  opposite. 


RULES  FOR  DRAGGING  147 

Drag  the  road  as  soon  after  a  rain  as  possible,  but  not  when  the  mud  is 
in  such  condition  as  to  stick  to  the  drag.  (It  might  also  be  added,  as  to 
ball  up.) 

Do  not  drag  a  dry  road. 

Drag  whenever  possible  at  all  seasons  of  the  year.  If  the  road  is 
dragged  immediately  before  a  cold  spell  it  will  freeze  in  a  smooth  con- 
dition. 

The  width  of  traveled  way  to  be  maintained  by  the  drag  should  be  from 
18  to  20  feet.  First  drag  a  little  more  than  a  single  wheel  track,  then 
gradually  increase  until  the  desired  width  is  obtained. 

Always 'drag  a  little  earth  toward  the  center  of  the  road  until  it  is  raised 
from  10  to  12  inches  above  the  edges  of  the  traveled  way. 

If  the  drag  cuts  too  deep,  shorten  the  hitch. 

The  amount  of  earth  that  the  drag  will  carry  along  can  be  very  con- 
siderably controlled  by  the  driver  according  as  he  stands  near  the  cutting 
end  or  away  from  it. 

When  the  roads  are  first  dragged  after  a  muddy  spell,  the  wagons  should 
drive  to  one  side,  if  possible,  until  the  roadway  has  a  chance  to  freeze  or 
partially  dry  cut. 

The  best  results  from  dragging  are  obtained  only  by  repeated  applica- 
tions. 

Remember  that  constant  attention  is  necessary  to  maintain  an  earth 
road  in  its  best  condition. 

Patrol  System  of  Maintenance. — This  means  that  the  roads 
are  separated  into  sections  and  some  one  person  detailed  to  look 
after  a  section.  The  patrol  or  overseer  is  supposed  to  go  over 
his  section  at  least  once  a  day  and  repair  any  tendency  to  form 
ruts.  He  looks  after  the  drainage,  cleans  the  ditches,  and  sees 
that  the  culverts  are  not  obstructed.  A  friendly  rivalry  is  soon 
engendered  between  neighboring  patrolmen  to  see  which  can 
have  the  best-kept  road.  Dragging  earth  roads  after  each  rain 
and  daily  attention  will  keep  them  in  usable  condition  and  the 
money  used  in  this  manner  will  be  well  spent. 

August  1,  1915,  the  state  of  Pennsylvania  placed  all  roads 
under  the  patrol  system.  The  following  list  of  general  duties 
of  the  patrolmen  has  been  prepared  by  the  State  Highway 
Department. 

Keep  drains  and  ditches  open  at  all  times. 

Special  'attention  must  be  given  to  defects  in  planking  and  the  condi- 
tion of  bridge  floors. 


148  EARTH  ROADS 

Repair  all  defects  in  the  surface  of  the  road,  maintaining  the  same  in  a 
true  and  even  condition. 

Repair  and  whitewash  all  guard  rails. 

Provide  protection  and  red  lights  in  cases  of  flood,  washouts,  or  any 
other  emergency  condition. 

Remove  brush  from  along  the  sides  of  the  road,  giving  special  attention 
to  this  condition  at  curves,  approaches  to  railway  crossings,  bridges,  cross- 
roads, etc. 

Keep  the  berms,  or  shoulders  of  the  road,  trimmed  up,  so  that  the  sur- 
face water  may  be  discharged  freely  from  the  road  surface  to  the  side 
ditches. 

Remove  all  advertising  signs  from  within  the  legal  limits  of  the  high- 
way. 

Paint  and  keep  in  first-class  condition  all  department  direction  and 
warning  signs. 

Inspect  culverts,  head  walls,  cribbing,  retaining  walls,  etc.,  and  report 
defects  immediately  to  the  superintendent. 

Whitewash  large' rocks  and  the  bases  of  poles  on  narrow  sections  of 
highways  and  at  sharp  curves  (spring  and  fall). 

The  poles  are  to  be  whitewashed  to  a  height  of  6  feet  above 
ground. 

All  equipment,  tools,  and  material  placed  in  charge  of  each  caretaker 
must  be  accounted  for  by  him  at  all  times,  and  all  tools  and  equipment 
kept  in  thorough  repair. 

Economic  and  workmanlike  results  will  be  the  most  important  factors 
recognized  by  the  department. 

Attention  must  be  given  to  the  entire  section  allotted  to  the  caretaker, 
and  work  not  confined  to  special  and  convenient  portions. 

When  working  on  the  road  the  caretaker  must  have  a  red  flag,  which 
will  be  supplied  by  the  department,  displayed  at  all  times  near  the  point 
where  work  is  being  performed. 

When  unusual  conditions  require  additional  help,  team  hire  or  material 
of  any  character,  permission  to  secure  same  must  first  be  obtained  from  the 
county  superintendent. 

A  daily  report  postal-card  must  be  mailed  every  evening  to  the  county 
superintendent . 

All  additional  help  and  team  hire  must  be  carried  on  foreman's  daily 
report  form,  etc. 

All  bills  for  material,  etc.,  in  amounts  less  than  $10  must  be  covered 
by  a  superintendent's  purchase  order,  and  larger  amounts  by  a  requisition 
of  the  superintendent  and  department  purchase  order. 

Caretakers  are  to  be  paid  an  hourly  rate  (Note. — At  present  15  to  20 
cents  per  hour),  and  full  value  in  service  will  be  exacted  for  Qvery  dollar 
expended. 


DUTIES  OF   PATROLMEN  149 

Caretakers  must  be  courteous  and  considerate  of  the  interests  of  the 
public  at  all  times,  and  conduct  themselves  in  a  manner  becoming  repre- 
sentatives of  this  Commonwealth. 

Sobriety,  honesty,  industry,  good  character  and  ability  are  the  essentials 
required,  and  a  failing  in  any  of  these  will  be  met  by  dismissal. 

The  patrol  system  has  been  adopted  by  Maryland,  Wis- 
consin, Michigan  and  in  modified  form  by  other  States. 


CHAPTER  VII 
SAND-CLAY  AND  TOP-SOIL  ROADS 

Theory  of  Sand-Clay  Roads. — Sand  being  composed  of  small 
particles  of  rock  that  are  only  slightly  subject  to  further  decom- 
position under  weather  conditions  has  in  itself  very  little  power 
of  cementation.  When  dampened  the  thin  film  of  water  which 
extends  from  one  grain  to  another  exerts  a  small  binding  force 
and  this  together  with  the  mechanical  bond  of  the  rough  par- 
ticles themselves  is  sufficient  to  hold  up  a  horse  or  wagon  with 
but  little  disarrangement  of  the  surface.  When  the  sand  is 
dry  and  the  binding  force  of  the  water  is  absent,  the  mechanical 
bond  being  inconsiderable,  the  horse  the  wagon  will  sink  in  a 
varying  distance  of  1  to  4  inches,  depending  on  the  character 
of  the  sand. 

If  the  sand  contains  clay,  feldspar,  or  rock  particles  capable 
of  further  chemical  reduction  under  the  action  of  water  or 
weather,  it  may  cement  into  a  more  or  less  monolithic  compo- 
sition. Clay,  being  composed  of  extremely  small  particles  of 
stone  dust,  so  small  that  the  particles  swim  more  or  less  freely 
in  the  film  of  moisture  surrounding  them,  has  practically  no 
mechanical  bond,  but  it  does  possess  a  small  cementing  prop- 
erty. This  property  is  manifest  only,  however,  when  the  clay 
is  in  a  rather  dry  condition.  Therefore,  sand  is  in  its  best  state 
for  road  purposes  when  wet;  clay,  when  dry.  A  mixture  of 
the  two  in  proper  proportions  furnishes  an  acceptable  road  sur- 
face for  both  wet  and  dry  weather.  The  mechanical  action  of 
the  sand  and  the  cementing  action  of  the  clay  assist  each  other 
just  as  in  a  gravel  or  a  macadam  road,  or  as  cement  and  aggre- 
gate in  concrete.  Again  clay,  being  extremely  small  particles, 
each  surrounded  by  its  film  of  water,  shrinks  on  drying  out 
much  more  than  sand,  the  particles  of  which  are  comparatively 
large.  This  may  be  illustrated  by  imagining  two  walls,  one 
laid  up  of  Roman  brick  1  inch  thick,  the  other  of  stone  blocks 

150 


PROPERTIES  OF  SAND  AND  CLAY  151 

1  foot  thick  having  mortar  joints  the  same  thickness  in  each. 
Now,  if  the  mortar  be  scraped  out  the  wall  of  bricks  will  decrease 
in  height  twelve  times  as  much  as  the  one  made  up  of  the 
thicker  stone  blocks.  As  sand  grains  may  vary  from  a  fraction 
to  1000  or  more  times  the  size  of  the  clay  particles  one  can  see 
how  the  shrinkage  will  differ.  Adding  coarse  sand  to  clay  will 
diminish  its  tendency  to  shrink  and  crack. 

When  surrounded  by  much  water  the  particles  of  clay  sep- 
arate and  float  in  the  water  quite  freely.     With  a  little  less 


FIG.  92.— A  Sand-Clay  Road. 

water  there  is  "slush";  with  still 'less  water,  "stickiness"; 
then  with  kneading  and  further  reduction  of  water  the  stickiness 
disappears  and  the  clay  is  plastic ;  with  still  further  reduction  of 
water  it  hardens  and  becomes  brittle  and  flours  or  rubs  off  like 
chalk.  On  the  other  hand  sand,  when  sufficiently  coarse,  has 
opposite  properties;  it  never  becomes  slushy  or  sticky  or 
plastic  or  cements  into  a  hard  brittle  body.  These  opposite 
tendencies  are  neutralized  by  mixing  the  sand  and  clay.  Slushi- 
ness  is  lessened,  stickiness  minimized,  and  the  mechanical  bond 
of  the  sand  and  the  cementing  action  of  the  clay  diminish  dis- 
integration and  disruption. 


152  SAND-CLAY  AND  TOP-SOIL  ROADS 

SELECTION  OF  MATERIALS 

While  for  road  purposes  clay  may  be  defined  as  earth  par- 
ticles of  extremely  small  size  (that  which  will  pass  a  200-mesh 
sieve)  the  properties,  of-  clays  differ.  Whether  this  is  due  to  the 
original  differences  of  the  rocks  from  which  the  clays  were 
decomposed  or  whether  it-  is  caused  by  the  intermixture  of 
organic  and  inorganic  foreign  substances  is  immaterial.  The 
road  man  is  concerned  only  with  the  question  whether  or  not 
they  can  be  used  for  road  purposes,  and  if  there  are  several 
varieties  available,  which  is  best.  Is  it  better  to  get  the  gumbo 
soil  from  the  bottom  land,  which  is  a  very  fine-grained  (non- 
gritty)  sticky  clay  strongly  impregnated  with  organic  matter, 
or  the  bank-clay  from  the  hills,  which  may  be  almost  pure 
kaolin?  Upon  this  method  of  classification,  practically  all  clays 
contain  sand  and  all  sands  clay.  In  making  up  a  mixture, 
therefore,  both  sand  and  clay  must  be  investigated.  Labora- 
tory and  field  tests  have  not  yet  been  standardized.  The  fol- 
lowing tests  may  be  made: 1  (1)  Separation  of  sand  and  clay, 
(2)  Mechanical  analysis  of  sand  content,  (3)  Slaking  test  on 
cylinder  of  sand-clay,  (4)  Examination  for  mica  and  feldspar, 
(5)  Slaking  test  or  clay  cylinder. 

Sampling. — Samples  should  be  taken  from  several  parts  of 
the  location  and  from  different  depths  in  the  bed. 

Separation  of  Sand  and  Clay. — 1st  Method. — The  sample  is 
first  thoroughly  dried  in  the  air  and  pulverized  with  a  wooden 
mallet.  Then  it  is  screened  through  a  10-mesh  sand  sieve,  and 
then  through  a  200-mesh  sieve.  Coarse  materials  except  grass, 
roots,  etc.,  caught  on  the  10-mesh  sieve  are  classified  as  gravel,2 
that  caught  on  the  200-mesh  sieve  as  sand,  and  that  passing 
the  200-mesh  sieve  as  clay. 

2d  Method. — Or  the  separation  of  sand  and  clay  may  be 
made  by  decantation  thus:  By  successive  quartering  a  portion 
of  about  150  grams  is  taken  and  dried  in  an  air  bath  at  100°  C. 
to  constant  weight;  100  grams  of  this  material  are  weighed  and 

1  "An  Investigation  of  Sand-clay  Mixtures  for  Road  Surfaces,"  by 
John  C.  Koch,  Trans.  Am.  Soc.  Civ.  Eng.,  Vol.  77,  p.  1454. 

2  Some  engineers  would  classify  all  passing  the  j-inch  sieve  as  sand. 


STANDARD   SAND-CLAY   MIXTURES  153 

placed  in  a  porcelain  evaporating  dish;  water  is  added  and  the 
sample  rubbed  well  until  the  clay  particles  are  in  suspension. 
The  clay  in  suspension  is  carefully  poured  off  and  more  water 
added;  the  process  is  repeated  until  there  is  faint  or  no  colora- 
tion of  the  water.  When  the  residue  is  stirred  up.  By  washing 
the  materials  properly,  practically  all  the  organic  matter,  silt  and 
clay  are  removed,  and  only  the  sand  particles  are  left,  with  possi- 
bly some  mica  and  feldspar.  The  residue  is  dried  and  weighed. 

Mechanical  Analysis  of  Sand. — The  dried  residue  in  the 
evaporating  dish  or  that  which  passes  the  10-mesh  sieve,  if  the 
first  method  is  used,  is  screened  through  the  200-,  100-,  60-, 
40-  and  20-mesh  sieves.  If  preferred,  they  may  be  taken  in 
reverse  order.  The  percentages  passing  the  several  sieves  can 
be  calculated  and  plotted. 

Professor  Koch's  1  studies  of  nearly  a  thousand  analyses 
has  led  him  to  the  following  conclusions: 

The  total  relative  sand  content,  disregarding  the  size  of  the  sand 
grains,  is  no  criterion  of  the  value  of  the  material. 

The  sand  smaller  than  No.  60  (passing  60-mesh  sieve)  is  of  little  value 
in  the  mixture,  that  smaller  than  No.  100,  except  in  very  small  quantities 
is  detrimental. 

The  greater  the  proportion  of  coarse  to  fine  sand,  the  harder  and  more 
durable  will  the  road  surface  be. 

For  the  best  possible  results  with  sand-clay  mixtures,  the  sand  smaller 
than  No.  10  and  larger  than  No.  60  should  not  be  less  than  60  per  cent  by 
dry  weight,  of  the  entire  sample.  In  addition,  the  smaller  than  No.  10 
and  larger  than  No.  60  should  be  composed  of  about  equal  parts  of  Nos. 
20,  40,  and  60.  The  total  sand  content  should  in  no  case  exceed  70  per 
cent  by  weight  of  the  total  sample. 

Standard    Sand-Clay    Mixtures. — From    experiments    and 
investigations  such  as  those  of  Professor  Koch  a  standard  mix- 
ture should  be  decided  upon.     The  following  might  answer  for  a 
I.  STANDARD  SAND-CLAY  MIXTURE 

Passing  200-mesh  sieve  39  per  cent 39  clay 

Passing  100-mesh  sieve  47  per  cent..   8  j 
Passing    60-mesh  sieve  55  per  cent..   8J 
Passing    40-mesh  sieve  70  per  cent. .  15 
Passing    20-mesh  sieve  85  per  cent..  15    45 
Passing    10-mesh  sieve  100  per  cent. .  15 

1  Ib.  Cit. 


154  SAND-CLAY  AND  TOP-SOIL  ROADS 

This  does  not  quite  satisfy  Professor  Koch's  idea  that  the  10,  20 
40  separations  should  together  be  60  per  cent.  There  is  no 
doubt  but  that  very  coarse  and  very  fine  materials  will  give 
best  results,  but  it  is  hard  to  find  such  a  combination.  If  a 
6  per  cent  allowance  on  either  side  of  the  above  standard  be 
made  there  results  the  following: 

II.  GOOD  SAND-CLAY  MIXTURES 

Passing  200-mesh  sieve 33  to  45  per  cent 

Passing  100-mesh  sieve .* 41  to  53  per  cent 

Passing    60-mesh  sieve 49  to  61  per  cent 

Passing    40-raesh  sieve 64  to  76  per  cent 

Passing    20-mesh  sieve 79  to  91  per  cent 

Passing    10-mesh  sieve. .  .  .  ! 100  per  cent 

If  there  is  material  that  will  not  pass  a  ten-mesh  sieve  its  use 
will  be  an  advantage  to  the  road  and  should  be  allowed  to  go  in 
with  the  rest. 

A.  S.  T.  M.  Specification.— At  the  1920  meeting  of  the 
American  Society  for  Testing  Materials  the  following  tentative 
specification  for  sand-clay  roads  was  submitted  by  the  Com- 
mittee on  Road  Materials: 

The  sand-clay  shall  be  composed  of  either  a  naturally  occurring  or 
artificially  prepared  mixture  of  hard,  durable,  preferably  angular,  frag- 
ments of  sand,  together  with  silt  and  clay  with  or  without  gravel,  and  shall 
be  free  from  an  excess  of  feldspar  or  mica. 

(a)  When  tested  by  means  of  laboratory  sieves  and  screens  the  sand- 
clay  or  gravel  shall  meet  the  following  requirements  for  grading: 

(6)  The  material,  if  any,  retained  on  a  j-inch  screen  shall  be  uniformly 
graded  from  the  maximum  size  present  to  |  inch. 

(c)  The  material  passing  a  Hnch  screen  shall  meet  the  following 
requirements : 

Per  cent 

Total  sand 50  to  80 

Sand  over  50-mesh  l 25  to  50 

silt :. .  -.. . ....... 5  to 20 

Clay 15  to  30 

1  For  specifications  for  this  sieve,  see  Standard  Method  for  Making  a 
Mechanical  Analysis  of  Sand,  or  Other  Fine  Highway  Material,  except  for 
Fine  Aggregates  Used  in  Cement  Concrete  (D7),  1918  Book  of  A.  S.  T.  M. 
Standards,  p.  663. 


PLOTTING  SIEVE  ANALYSES 


155 


A  STRAIGHT  LINE  METHOD  OF  PLOTTING  SIEVE  ANALYSES 

Table  II  may  readily  be  plotted  thus:  On  a  sheet  of  ruled 
writing  paper  number  spaces  OA,  Fig.  93,  to  represent  the 
percentage  passing  the  sieves.  Draw  a  diagonal  line  ON,  then 
NB  perpendicular  to  OB.  Draw  perpendiculars  CD,  EF,  etc., 
so  they  will  cut  the  diagonal  ON  at  heights  indicated  by  stand- 
ard sieve  separations.  Thus,  that  for  the  200-mesh  sieve,  CD, 


10 

100 


0  S(ere   Number      200     100       60 

Percent   Passing      39      47       55  70  85 

Standard  Mixture 

FIG.  93.— Straight-line  Plot  of  Sieve  Analysis. 


will  cut  it  at  a  point  39  per  cent  up,  Table  I;  the  100-mesh  sieve 
EF,  at  47  per  cent,  etc.  Draw  lines  6  per  cent  above  and  below 
ON.  The  shaded  area  covers  the  grading  given  in  Table  II. 
Any  loam  or  other  natural  mixture  may  be  readily  compared 
with  the  standard  by  making  a  sieve  analysis  and  plotting  on 
this  diagram.  Thus  a  natural  mixture  of  top-soil  (Professor 
Koch's  No.  150)  which  has  given  excellent  results  shows  the 
following  percentages  of  amount  smaller  than  No.  10  separation 
retained  upon  the  several  sieves: 


156 


SAND-CLAY  AND  TOP-SOIL  ROADS 


Sieve  No 

Per  cent  retained .  . 


10      20 
6.313.7 


40     | 60     | 80 
16.6)17.7]  7.5 


100 
2.3 


Sand  dust 
11.5 


Clay 
30.7 


The  percentages  passing  the  sieves  arranged  for  plotting  are: 


Sieve  No j     10 

Per  cent  passing |  100 


20 

86.3 


40 
69.7 


60 
52.0 


80 
44.5 


100 
42.2 


200 
30.7 


This  is  plotted  on  Fig.  93,  broken  line.  It  will  be  noticed  that 
it  everywhere  falls  within  the  shaded  area  (except  No.  200) 
as  might  be  seen  by  noting  that  the  separation  percentage 
nowhere  varies  more  than  6  per  cent  from  the  standard  assumed. 

Method  of  Proportioning. — Having  adopted  a  standard  and 
drawn  the  vertical  lines  to  represent  the  several  sieve  separa- 
tions the  diagram  may  be  used  to  ascertain  the  proper  propor- 
tions of  a  mixture  of  two  or  more  sands,  clays  or  soils. 

To  illustrate,  in  a  certain  locality  is  a  road  with  a  sand  spot 
in  it.  Clay  is  obtainable  at  a  distance  of  several  miles  and 
sand  and  loam  near  by,  having  the  following  analyses  re- 
spectively : 


Percentage  passing  and  retained  on  next  finer  sieve 


200 

100 

60 

40 

20 

10 

Clay  
Silt  Loam  
Sand  

88.2 
40.8 
1.0 

10.8 
33.7 
2.0 

0.9 
19.9 
12.5 

0.0 
2.0 
21  0 

0.1 
1.9 
34  5 

0.0 
1.7 
29  0 

Calculating  the  total  percentages  passing  the  several  sieves 
and  plotting  on  the  diagram  gives  Fig.  94. 

Note  that  a  mixture  of  1  clay  to  1  sand  approximately 
agrees  with  the  standard  adopted.  The  mixture  may  be 
computed  thus: 

It  might  be  the  part  of  wisdom,  however,  to  use  the  silt  loam 
in  connection  with  the  sand  and  clay.  A  proportion  of  1  clay: 
3  loam  :  3  sand  gives  the  mixture  shown  in  the  last  column  and  E 
of  the  plot.  This  is  almost  as  good  a  mixture  and  it  ought  to  be 
much  cheaper  than  the  material  which  has  to  be  hauled  a  long 


PROPORTIONING   MIXTURES 


157 


Mix  ABC 

A 

B 

C 

Sum 

Ave.= 

Ave.  = 

Clay 

Silt  loam 

Sand 

A+C 

Sum  -T-  2 

A+3B+3C 

• 

7 

200-mesh  .  .  . 

88.2 

40.8 

1.0 

89.2 

44.6 

30.5 

100-mesh  .  .  . 

99.0 

74.5 

3.0 

102.0 

51.0 

47.8 

60-mesh.  .  . 

99.9 

94.4 

15.5 

115.4 

57.7 

61.4 

40-mesh.  .  . 

99.9 

96.4 

36.5 

136.4 

68.2 

71.1 

20-mesh  .  .  . 

100.0 

98.3 

71.0 

171.0 

85.5 

86.8 

10-mesh.  .  . 

100.0 

100.0     |  100.0 

200.0 

100.0 

100.0 

distance;   clay  is  reduced  from  one-half  to  one-seventh  of  the 
volume  of  the  road  surface. 


10 


Clay,  A 


Silt  Loam,  B 


A  :  C  :  :  1  :  1,  D 


A:  B:C:  :  1  : 


Sand,  C 


Siere  200 

Siunaurd          39 


100 
47 


10 
100 


FIG.  94.—  Plot  of  Sand-Clay  Mixtures. 


So  far  it  has  seemed  easy  to  get  mixtures  plotting  sufficiently 
near  to  the  adopted  standard.  It  may  not  always  be  practi- 
cable to  get  materials  that  will  thus  agree.  Take,  for  example, 
an  analysis  of  dune  sand  from  the  sand-hill  region  of  western 
Nebraska,  Table  III,  Fig.  95.  This  sand  covers  a  region  of 


158 


SAND-CLAY  AND  TOP-SOIL   ROADS 


many  square  miles  in  western  Nebraska,  extending  into  western 
Kansas,  western  Dakota,  eastern  Wyoming  and  eastern  Colo- 
rado. And  while  it  is  naturally  covered  with  bunch  grass  sod, 
this  is  soon  destroyed  by  travel,  leaving  the  roadway  a  pure 
sand  bed  through  which  it  is  very  difficult  to  draw  a  vehicle. 
This  sand,  yellowish,  or  brownish-gray,  is  remarkably  smooth 
and  round  and  uniformly  fine  or  medium  in  "size.  There  is  very 
little  coarse  material  or  material  sufficiently  fine  to  be  called 


90 
80 
70 
60 
50 
40 
30 
20 
10 
0 

' 

«*~~* 

'""/I 

j 

i 
i 

/ 

2^ 

(     ! 

I 
i 

j 

// 

~/jjr 

1 

/ 

j// 

i 

i 

Bassett  Clay     c 

/ 

ft 

/ 

i 

/ 

'// 

/  i 

j 

.// 

/ 

'/ 

j 
j 

•7  A 

/ 

I 

/  ! 

1 

} 
/ 

1 

/              Dune  Sand- 
f                 Atkinson    Sand  ( 

7i 

,.-C 
Y~~ 

/"' 

200     100      60              40              20              10 
Adopted  Standard    39      47      55               70              85             1(X 

FIG.  95. — A  Mixture  of  Nebraska  Dune  Sand,  Bassett  Clay,  Atkinson 
Sand  in  Proportions  of  1  :  1  :  2. 

clay.  Mechanical  stability  and  binding  qualities  are  both 
lacking.  To  make  good  roads  of  this  sand  will  require  a  strong 
binder  such  as  bitumen  with  some  method  of  procuring  a  sound 
foundation.  To  make  a  good  sand-clay  road  of  this  material 
will  require  additional  coarse  sand  and  fine  clay  in  order  to 
balance  the  mixture.  Both  these  materials  are  exceedingly 
scarce  in  the  sand-hill  region.  In  the  table  a  combination  of 
Bassett  clay  and  Atkinson  coarse  sand  is  worked  out.  While 
this  is  not  the  best  of  sand-clay  roads  it  will  give  fair  results.  A 


TESTS   OF  SAND-CLAY   MIXTURES 


159 


TABLE  III 


• 

1  Dune  Sand, 

Dune 

Bassett- 

Atkin- 

2 Bassett 

Sand  ' 

Clay2 

son  Sand 

Clay,  1  At- 

kinson Sand 

200-mesh  .  .  . 

,     1.5 

1.5 

56.5 

0.1 

28.6 

28.6 

100-mesh..  . 

9.2 

10.7 

10.9 

0.5 

7.9 

36.5 

60-mesh  .  .  . 

50.0 

60.7 

23.4 

3.0 

25.0 

61.5 

40-mesh.  .  . 

34.7 

95.4 

4.0 

10.0 

13.2 

74.7 

20-mesh  .  .  . 

3.8 

99.2 

2.7 

36.4 

11.4 

86.1 

10-mesh.  .  . 

.8 

100.0 

2.5 

50.0 

13.9 

100.0 

• 

100.0 

Dune  sands  vary  in  texture  as  other  sands: 


Dune  sands  from: 

200 

100 

60 

40 

20 

10 

Wood  Lake  
Halsey  

1 
1 

8 
8 

64 
46 

25 
38 

2 
6 

0 
1 

2 

12 

38 

44 

3 

1 

Cody 

2 

9 

52 

32 

4 

1 

Total  
Average  

6 
1.5 

37 
9.2 

200 
50 

139 
34.7 

15 

3.8 

3 
.8 

2  Found  at  Bassett,  Stuart,  Newport  and  other  places  along  the  Elkhorn  River. 

little  richer  clay  having  not  quite  so  much  sand  would  be 
better.  These  were  selected  because  they  occur  near  together. 
The  Atkinson  sand  as  found  is  about  one-fifth  gravel  larger  than 
a  10-mesh  separation.  This  should  be  allowed  to  go  in. 

Other  Tests. — In  addition  to  the  sieve  tests  other  tests  may 
be  employed  to  confirm  or  modify  the  mixtures  tentatively 
decided  upon. 

Slaking  Test. — Two  methods  for  making  this  test  have  been 
suggested  but  they  do  not  differ  in  principle. 

Koch's  Method. — A  test  cylinder,  1  inch  in  diameter  and 
3  inches  long  is  made  of  the  material  passing  the  No.  10  sieve 
by  wetting  it  sufficiently  to  make  a  very  stiff  paste  and  after 


160  SAND-CLAY  AND  TOP-SOIL  ROADS 

working  it  thoroughly  together  packing  it  in  a  metal  mold 
with  a  tight  filling  plunger  and  a  mallet.  The  cylinder  is  dried 
to  constant  weight  in  an  air  bath  at  100°  C.  When  entirely 
cooled  it  is  immersed  in  a  glass  jar  of  water  at  a  temperature  of 
21°  C.  and  the  time  noted  for  its  complete  disintegration.  Dis- 
integration is  supposed  to  be  complete  when  the  cylinder  has 
broken  down  until  the  material  is  standing  approximately  at 
its  natural  slope  of  repose.  Professor  Koch  says,  "  In  sand- 
clay  mixtures  which  have  given  satisfactory  service  the  time  to 
disintegrate  completely  varies  from  two  minutes  to  nearly  one 
hour.  This  test  will  give  a  fairly  good  idea  of  the  resistance  of 
any  sand-clay  mixture  to  the  action  of  water.  The  most  durable 
mixtures,  in  general,  are  those  which  take  longest  to  disin- 
tegrate." 

The  same  test  is  applied  to  clay  alone  and  the  slaking 
time  of  good  clay  cylinders  varies  from  two  minutes  to  twenty 
minutes.  The  sand  may  be  mixed  with  clay  in  varying  propor- 
tions and  the  times  of  slaking  compared. 

James'  Field  Test.1 — Mixtures  are  made  ranging  from  1  part 
sand  to  3  parts  clay,  up  to  3  parts  sand  and  1  part  clay,  varving 
by  one-half  of  one  part: 


Sand !  1 

Clay |  3 


1        1 

2  I  a 


1     I  H 

1     i  1 


2j 

1 


Equal  samples  are  taken  from  the  several  test-mixtures  with  a 
small  measure.  These  are  wetted  and  mixed  to  a  stiff  paste 
and  rolled  between  the  palms  of  the  hands  into  reasonably  true 
spheres  and  placed  in  the  sun  to  dry.  Designating  marks  may 
be  placed  on  them.  When  dry  they  are  placed  in  a  circle  in  a 
flat  pan  or  dish,  and  enough  water  poured  in  the  pan  to  cover 
them,  care  being  taken  not  to  pour  the  water  directly  upon  the 
samples.  Slaking  will  begin  at  once  and  proceed  at  different 
rates.  The  sandy  specimens  will  break  down  first,  those  with 
excessive  clay  will  disintegrate  second  and  those  having  about 
the  proper  proportions  will  act  more  slowly.  Usually  there  will 
be  one  or  two  that  determine  the  proper  proportions. 

1  Transactions  Am.  Soc.  Civ.  Eng.,  Vol.  77,  p.  1482. 


CONSTRUCTING   SAND-CLAY   ROADS  161 

Flouring  Test. — Dry  spheres,  cubes,  or  pats  made  up  of 
the  mixtures  and  dried  are  lightly  rubbed  with  the  thumb 
and  finger.  Those  having  too  much  sand  will  break  down  rap- 
idly; those  having  too  much  clay  will  soon  begin  to  "flour" 
or  "  dust  "  away,  while  those  having  the  most  suitable  mixtures 
will  assume  a  slightly  glazed  effect  under  the  light  rubbing  due 
to  the  moisture  and  oil  of  the  skin.  As  a  rule  select  the  sample 
having  next  more  sand  than  the  one  which  glazes. 

Test  for  Mica  and  Feldspar. — Examination  of  the  sand  with 
a  small  powered  microscope  will  show  mica  or  feldspar.  Or 
they  may  be  separated  by  water,  the  mica  and  feldspar  being  of 
lower  specific  gravity  than  quartz. 

If  mica  exists  in  proportion,  less  than  5  per  cent,  no  harm 
will  ensue.  Above  that  it  acts  as  a  lubricant  and  prevents  con- 
solidation of  the  road.  Feldspar  will  do  little  damage,  unless 
in  greater  proportion  than  3  or  10  per  cent,  when  the  road  will 
cut  and  wash  easily. 

CONSTRUCTING  SAND-CLAY  ROADS 

Sand-clay  roads  as  far  as  construction  is  concerned  are  of 
two  kinds — clay  roads  upon  which  sand  is  to  be  put  and  sand 
roads  upon  which, clay  is  to  be  put.  The  first  might  be  called 
sanded  roads. 

Sanded  Roads. — After  the  sand  is  selected  it  is  a  good  plan 
according  to  W.  L.  Spoon,  Office  of  Public  Roads,  Circular 
No.  61,  to  haul  it,  in  advance  alongside  the  road  which  is  to 
be  improved.  When  the  road  softens  a  quantity  of  sand  should 
be  spread  broadcast  over  the  traveled  roadway  for  the  desired 
width  until  the  softened  clay  surface  of  the  road  is  saturated 
with  the  sand.  In  this  way  the  advantage  of  hauling  the  sand 
on  a  firm,  dry  clay  road  is  obtained,  and  it  is  ready  for  use  when 
the  road  is  softened  by  rain  and  slightly  cut  by  travel.  For  a 
first  application  the  material  should  be  mixed  to  a  depth  of  from 
5  to  8  inches  according  to  the  amount  of  traffic.  Loose  material 
will  shrink  30  to  40  per  cent  in  the  process  of  packing.  As  the 
road  dries  somewhat  it  should  be  smoothed  by  dragging.  The 


162 


SAND-CLAY  AND  TOP-SOIL  ROADS 


road  will  require  constant  attention  for  a  year  or  more;   mud 
holes,  sand  pockets,  and  ruts  should  be  filled  after  each  rain. 

Clayed  Roads. — The  roadbed  having  been  prepared  by 
plowing  and  scraping  the  sand  from  the  center  of  the  road,  Fig. 
96,  and  piling  it  up  along  the  side,  the  clay  is  placed  in  a  uniform 
layer  in  the  trench  thus  dug.  This  should  be  begun  at  the  end 
of  the  road  nearest  the  store  of  clay  in  order  that  the  teams  may 
walk  over  the  harder  clay.  After  depositing  the  clay  the  sand 


...'....    .    .,. 


Sand  plowed  out  and   clay  deposited. 


Sand  brought  bach  upon  the  clay,   mixed  by  plowing 
and  harrowing  then  shaped  with  the  grader. 


With  traffic  and  dragging  the  clay  will  work  down  and  mix  with 
the  sand  of  the  shoulders  until  final  cross-section  is  something  like  this. 

FIG.  96. — Claying  a  Sand  Road. 


on  the  sides  is  spread  over  the  top  to  a  depth  of  about  2  to  4 
inches  and  the  whole  plowed  and  harrowed  or  disked  so  as  to 
mix  thoroughly  the  sand  and  clay.  Finally  the  road  is  shaped 
and  smoothed  with  the  grader  and  drag.  Traffic  will  work  the 
clay  at  the  center  toward  the  edge.  The  drag  will  pull  some 
sand  from  the  edge  back  with  this  toward  the  center.  With 
care,  adding  a  little  clay  where  needed  the  road  may  be  made 
to  take  a  form  having  a  thick  mass  of  sand  clay  mixture  in  the 


TOP-SOIL   ROADS 


163 


center  to  a  feather  edge  at  the  sides.  Side  ditches  should  not 
be  very  deep.  If  the  roadway  is  crowned  about  1  inch  to  the 
foot  rainwater  falling  upon  the  road  will  be  carried  to  the  sandy 
edge  where  it  soon  soaks  into  the  soil.  If  the  sand  beneath  the 
clay  does  remain  a  little  damp  it  will  add  firmness  to  the  foun- 
dation and  prevent  flouring  of  the  clay  mixture. 

Top-soil  Roads.  —  Fig.  97  shows  a  form  of  cross-section  used 
for  top-soil  roads  in  Georgia.  A  top-soil  road  is  one  whose 
wearing  coat  is  composed  of  top-soil  which  has  been  found  by 
experience  or  examination  to  have  about  the  requisite  combina- 
tion of  sand  and  clay  to  form  a  good  road. 

The  road  surface  is  shaped  and  plowed  then  a  layer  of  top- 


2" 


1  I 

Cross-section,  Sand  Clay  Rood  before  Consolidation 


Cross-section,  Sand  Clay  Rood  after  Consolidation   I 
FIG.  97.— Top-soil  Roads. 


soil  10  to  12  inches  thick  is  deposited  uniformly.  Earth  from 
the  shoulders  and  ditch  brought  against  this  and  the  whole 
shaped  with  the  grader.  Rolling  is  frequently  dispensed  with 
as  the  teaming,  while  hauling  the  material  and  subsequent 
traffic  soon  accomplish  consolidation.  In  Alabama  the  speci- 
fications call  for  dumping  the  top-soil  "  on  the  road  with  three 
or  more  loads  opposite  each  other;  the  distance  between  the 
loads  depending  on  the  width  and  thickness  of  the  top-soil. 
The  loads  should  be  dumped  in  this  way  in  three  or  more  parallel 
lines  until  a  hundred  or  so  feet  have  been  dumped.  The  shaping 
of  the  top-soil  should  be  commenced  before  the  individual  load 
begins  to  pack."  Other  engineers  believe  it  better  to  spread 


164  SAND-CLAY  AND  TOP-SOIL  ROADS 

the  soil  as  the  loads  are  dumped  because  the  settlement  is  more 
uniform. 

Also,  in  Alabama  "  If  the  surfacing  used  is  not  a  good  nat- 
ural mixture  of  sand  and  clay  the  mixture  will  have  to  be  made 
on  the  road  in  the  following  manner:  On  a  clay  foundation  the 
subgrade  must  be  plowed  up  to  a  depth  of  4  inches,  all  clods 
being  thoroughly  pulverized  by  harrowing  or  otherwise,  and 
sand  spread  on  to  a  depth  of  6  inches,  the  mass  shall  then  be 
mixed  and  puddled  by  turning  with  a  plow  and  using  a  disk- 
harrow  and  dressed  up  with  the  road  machine.  On  a  sandy 
foundation  the  sand  must  be  plowed  to  a  depth  of  6  inches  and 
a  suitable  clay  spread  to  a  depth  of  4  inches  and  mixed  as  above 
described.  The  mixing  and  puddling  process  must  be  kept  up 
from  time  to  time  until  a  good  mixture  is  obtained  and  the 
road  packs  firm  and  hard  and  is  true  to  grade  and  cross-section 
and  free  from  holes  and  bumps." 

MAINTENANCE 

The  maintenance  of  a  sand-clay  road  is  similar  to  that  of  an 
earth  road  and  consists  in  dragging  after  rains.  It  will  be 
found,  however,  that  with  a  good  mixture,  the  surface  will 
become  so  hard  that  a  light  drag  will  not  remove  the  bumps.  A 
steel  or  heavy  drag  will  be  required.  The  road-grader  followed 
by  a  drag  will  be  found  effective.  The  blade  of  the  grader 
should  be  set  so  as  merely  to  cut  off  the  projecting  hard  bumps ; 
the  drag  does  the  filling  in  and  smoothing.  Fresh  material 
similar  to  the  wearing  surface  will  have  to  be  brought  occa- 
sionally to  fill  in  ruts  or  holes  where  the  surface  has  broken 
through  or-  worn  out.  With  constant  care  a  sand-clay  road 
should  give  satisfactory  results  for  a  great  many  years.  Of 
course,  when  it  has  worn  through  a  new  road  may  have  to  be 
constructed,  as  with  any  other  material. 

Cost. — Sand-clay-  roads  cost  more  than  earth  roads  and 
usually  less  than  macadam  or  even  gravel.  W.  L.  Spoon  of 
the  U.  S.  Office  of  Public  Roads,  Farmers'  Bulletin  311,  gives 
the  following  as  approximate  costs  of  constructing  1  rnile  of  a 


COST  OF  SAND-CLAY  ROADS  165 

12-foot  sand-clay  .road  on  the  assumption  that  clay  can  be 
procured  within  a  mile  of  the  road  which  is  to  be  improved, 
and  that  the  cost  of  labor  is  about  $1  per  day  and  teams  $3 
per  day: 

Crowning  and  shaping  with  road  machine,  using  two  teams  at 

$3  per  day  and  1  operator  at  $1 .50  per  day  for  1  day $7 . 50 

Loosening  1,173^  cubic  yards  of  clay  with  pick  and  shoveling  into 

wagons  at  15  cents  per  cubic  yard 176.00 

Hauling  1173-J  cubic  yards  of  clay,  at  23  cents  per  cubic  yard..  .  .  269.86 
Spreading  clay  with  road  machine,  using  2  teams  at  $3  and  expert 

operator  at  $1.50  per  day  for  three  days 22 . 50 

Shoveling  sand  on  clay,  estimated  at  \  cent  per  square  yard 35 . 20 

Plowing,  using  1  team  at  $3  per  day  for  four  days 12 . 00 

Harrowing,  using  1  team  at  $3  per  day  for  two  days 6 . 00 

Shaping  and  dressing  with  road  machine,  using  two  teams  at  $3 

and  expert  operator  at  $1.50  per  day  for  two  days 15. 00 

Rolling  estimated  at  \  cent  per  square  yard 35.20 


Total $579.26 

Estimated  cost  $579.26  per  mile  or  8  cents  per  square  yard 

The  Office  of  Public  Roads  gives  as  its  experience  the  cost 
of  sand-clay  roads  to  range  from  $200  to  $1200  per  mile,  in 
most  cases  running  from  "$300  to  $800.  At  Gainesville,  Fla.,  a 
14-foot  roadway,  9  inches  thick  cost  $881.25  per  mile  or  10. 
cents  per  square  yard;  at  Tallahassee,  Fla.,  a  16-foot  roadway 
7  inches  thick  cost  $470  or  5  cents  per  square  yard ;  at  Marion, 
Ala.,  11  to  22  cents.  At  Columbus,  Neb.,  detailed  costs  for 
3002  feet  of  sand-gumbo  road  graded  24  feet  in  cuts  and  32  feet 
on  fills,  with  sand-gumbo  surface  16  feet  wide  are  given  in 
the  table  on  p.  166.  (Bulletin  53,  U.  S.  Department  of  Agri- 
culture, Office  of  Public  Roads.) 

Here  both  sand  and  gumbo  were  brought  upon  the  road; 
the  gumbo  was  hauled  approximately  2  miles,  the  sand  4000  feet. 
The  gumbo  was  spread  to  a  depth  of  7|  inches,  and  the  sand  to  a 
depth  of  6  inches,  both  measured  loose.  The  two  materials 
were  then  mixed  by  means  of  plows  and  harrows  and  shaped 
with  a  steel  drag  and  road  machine. 


166 


SAND-CLAY  AND  TOP-SOIL  ROADS 


Earthwork 

Amount 

Unit  Cost 
Per  Cubic 
Yard 

Unit  Cost 
Per  Square 
Yard  Wear- 
ing Surface 

760  cubic  yards  excavation  
Shoulders  and  ditches 

$120.00 
46  40 

0.158 

0.0225 
0  0088 

5  337  square  yards  shaping  subgrade 

28  20 

0  0052 

Miscellaneous.        

1  40 

0.0002 

Superintendence 

4  20 

0  0008 

Total                                   

$200  .  20 

0.0375 

Sand-gumbo  wearing  surface: 
Purchase  of  gumbo  pit 

41  35 

0  035 

0  008 

Loading  gumbo  

180.40 

0.155 

0.034 

Hauling  gumbo.             

698  80 

0  600 

0.131 

Spreading  gumbo 

34  00 

0  029 

0  006 

Loading  sand  
Hauling  sand                             

93.60 
299  00 

0.105 
0  336 

0.018 
0.056 

Mixing  sand  and  gumbo  
Shaping           .        

37.20 
4  00 

0.018 

0.007 
0.0025 

Rolling 

13  60 

0  001 

Miscellaneous 

12  60 

0  002 

Superintendence                

37  80 

t).007 

Total                   .    .'  

$1462  .  95 

0.2745 

Grand  total 

$1663.15 

0.3120 

CHAPTER  VIII 
GRAVEL  ROADS 

GRAVEL  is  defined  as  an  aggregate  of  small  naturally  formed 
stones  or  pebbles  usually  found  in  deposits  more  or  less  inter- 
mixed with  sand  and  clay  but  in  which  mixture  those  particles 
that  will  not  pass  a  10-mesh  sieve  predominate.  The  dif- 
ferentiation between  gravel,  sand,  silt,  and  clay  should  be  made 
on  the  following  basis: 

Retained  on  a  10-mesh  sieve Gravel 1 

Passing  a  10-mesh  and  held  on  a  200-mesh  sieve .  .   Sand 
Passing  a  200-mesh  sieve Clay  and  silt 

Gravel  is  nearly  always  made  up  of  pebbles  which  have 
been  more  or  less  rounded  by  the  action  of  water  and  weather 
and  the  mechanical  grinding  of  one  particle  of  stone  against 
another.  Some  so-called  gravels  are  small  angular  fragments 
of  broken  rock  which  have  not  yet  become  rounded.  Such  is 
the  gravel,  or  rather,  "  disintegrated  granite  "  of  Sherman  Hill, 
Wyo.,  and  other  places  in  the  West.  This  material  lies  in  thick 
beds  and  when  taken  out  with  a  steam  shovel  the  walls  stand 
perpendicular  for  20  or  30  feet.  It  is  extensively  used  for  bal- 
last and  depot  platforms  by  the  Union  Pacific  railroad,  and  has 
also  been  used  for  road  purposes  with  success. 

The  kind  of  gravel  commonly  utilized  for  roads  is  made  up 
of  the  rounded  water  worn  pebbles  and  this  is  what  will  be 
meant  hereafter  when  the  word  "  gravel  "  is  used  without  mod- 
ification. Such  gravel  is  generally  hard  and  durable  and  when 

1  Recommended  by  committees  of  the  Am.  Soc.  for  Testing  Materials 
and  the  Am.  Soc.  of  Civ.  Eng.  Many  engineers  believe  this  separation 
should  be  made  on  the  |-inch  screen. 

167 


168 


GRAVEL  ROADS 


properly  graded  in  size  forms  excellent  road-making  material. 
In  addition  to  a  graded  mixture  of  gravel  there  must  be  present  a 
binder  of  fine  dust  or  some  other  material  that  will  grind  or 
decompose  into  a  cementing  factor.  For,  while  with  the  larger 
and  more  angular  particles  stability  is  obtained  by  mechanical 
bond,  still,  as  in  sand-clay  roads,  the  cementing  power  of  the 
dust,  though  weak,  is  the  final  requisite  of  success. 

MECHANICAL  ANALYSES  CURVES  DEFINED 

The  gravel  having  been  separated  by  screens,  sieves,  or 
otherwise  into  several  parts  determined  by  the  size  of  the  par- 
ticles a  curve  is  plotted  with  the  sizes  of  the  sieve  openings,  or 
particles,  as  abscissas  and  the  percentage-  passing  the  several 
sieves  as  ordinates.  This  is  a  mechanical  analysis,  or  granu- 
lometric  analysis  of  the  material.  Woven  brass  wire  sieves  are 
used  for  separating  the  sand  and  screens  the  gravel. 

TABLE  I 


Meshes  Per  Linear 
Inch 

Diameter  of  Wire, 
.  .    Inches 

Approximate  Size  of  Open- 
ing, Inches 

10 

0.027 

0.073 

20 

0.0165 

0.0335 

30  l 

0.01375  (0.011) 

0.01958  (0.022) 

40 

0.01025 

0.01475 

50 

0.009 

0.011 

80 

0.00575 

0.00675 

100 

0.0045 

0.0065 

2001 

0.00235  (0.0021) 

0.00265  (0.0029) 

1  The  standard  200-mesh  cement  sieve  of  the  U.  S.  Bureau  of  Standards,  which  is  now 
also  the  standard  for  the  A.  S.  T.  M.,  has  a  diameter  of  wire  of  0.0021  and  a  nominal 
opening  of  0.0029.  Also  the  A.  S.  C.  E.,  the  U.  S.  War  Department  and  the  A.  S.  T.  M. 
standard  No.  30  sieve  for  grading  sand  for  cement  testing  has  a  wire  diameter  of  0.011 
with  a  nominal  opening  of  0.022. 

Sieves. — A  standard  sieve  is  8  inches  in  diameter  and  2i 
inches  high.  The  number  of  meshes  per  lineal  inch  varies  from 
10  to  200.  Since  the  wires  occupy  space  it  is  necessary  to 


SAND  AND   GRAVEL  SIEVES  169 

determine  the  actual  size  of  the  openings  in  order  to  obtain  the 
sizes  of  the  separations  made  by  the  several  sieves.  These  have 
been  standardized  by  the  American  Society  for  Testing  Mate- 
rials 1  and  are  manufactured  with  such  accuracy  that  they  will 
not  vary  greatly  from  these  standards.  The  table  gives  the 
A.  S.  T.  M.  standard  as  to  number  of  meshes  and  size  of  wires, 
to  this  has  been  added  the  third  column  giving  the  calculated 
nominal  or  approximate  opening. 

Calibrating  Sieves.  —  Sieves  should  be  examined  occasionally 
to  see  if  they  correspond  with  these  sizes,  and  that  the  wires 
have  not  become  displaced.  The  meshes  or  openings  should  be 
perfect  squares.  There  are  two  ways  of  calibrating  sieves  — 
first,  the  actual  size  of  the  opening  is  observed  by  means  of  a 
microscope  and  micrometer;  second,  a  number,  100  or  200, 
grains  of  the  last  sand  that  passes  through  in  sifting  a  sample 
are  counted  and  weighed.  Knowing  the  specific  gravity  of  the 
sand,  the  diameter  of  the  grains  can  be  calculated  by  the  formula 


where   d  represents  the  diameter  of  the  grain  in  cm.  ; 
W,  the  weight  of  the  counted  grains  in  gm.  ; 
S,  the  specific  gravity  of  the  sand,  approximately  2.65; 
n,  the  number  of  grains  in  W', 
TT,  the  abstract  number  3.1416 

The  difference  between  d  and  the  size  of  the  opening  where  a 
round  well-worn  sand  has.  been  used  is  inconsiderable.  The 
former  of  the  two  methods  given  is  better  adapted  to  cali- 
brating the  fine  sieves  and  the  latter  the  coarse  sieves. 

The  commercial  number  of  a  sand  sieve  is  the  number  of 
meshes  or  openings  between  wires  per  lineal  inch.  In  gravel 
screens  the  openings  are  drilled  round  holes  of  the  given  diam- 
eter. 

Density.  —  The  more  dense  the  mixture  of  gravel,  sand  and 

i  A.  S.  T.  M.  Standards,  1916,  p.  535. 


170 


GRAVEL  ROADS 


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N   i—  I                  C^l   I-H   i—  I 

8 

O    TjH     00                        Tf< 

CO  (N   1-1                 (N 

O   lO                  C^   OO   ^ 

C^    i-H                       C^    i—  1    T-H 

8 

rt<   O   »O                 O 
(N   (N   1-1                 (N 

>  TP             oo  co  co 

^ 

Largest  stone,  1  inch: 
Upper  limit  
Medium  
Lower  limit  

Largest  stone,  2  inches 
Upper  limit  

Medium  
Lower  limit  

Largest  stone,  3  inches 
Upper  limit  
Medium  
Lower  limit  

GRADING   ROAD   GRAVEL  171 

clay  the  better  the  result.  W.  B.  Fuller  and  S.  E.  Thompson  1 
proposed  a  maximum  density  theory  for  proportioning  concrete 
aggregate  which  is,  briefly,  that  "  the  best  mixture  of  cement 
and  aggregate  has  a  mechanical  analysis  curve  resembling  a 
parabola,  which  is  a  combination  of  a  curve  approaching  an 
ellipse  for  the  sand  portion  and  a  tangent  straight  line  for  the 
stone  portion.  The  ellipse  runs  to  a  diameter  of  one-tenth  of 
the  maximum  size  of  stone,  and  the  stone  from  this  point  is 
uniformly  graded." 

Table  II  is  worked  out  on  the  Fuller-Thompson  theory  and 
may  be  used  as  a  rough  guide  for  getting  a  well-graded  mixture 
of  gravel  for  road  purposes.  For  the  method  of  making  up 
mixtures  see  Chapter  XII,  Concrete  Roads. 

GREAT  REFINEMENT  IN  GRADING  NOT  NECESSARY 

Good  roads  have  been  made  of  gravel,  varying  greatly  from 
the  above-mentioned  maximum  density  curves.  Especially  is 
this  true  where  a  coarser  gravel  is  used;  the  traffic  grinds  off 
the  gravel  itself  or  tracks  on  from  the  side  sufficient  "  fines  "  to 
act  as  a  binder.  While  gravel  has  been  used  longer  than  any 
other  material  for  hardening  roads  it,  notwithstanding,  has  been 
used  in  a  more  or  less  careless,  manner  the  gravel  most  con- 
venient being  hauled  and  dumped  upon  the  road  surface,  trusting 
to  time  and  traffic  for  the  hardening.  Therefore,  in  trying  to 
fix  upon  a  standard  grading  for  gravel  roads,  it  does  not  seem 
wise,  with  our  present  lack  of  knowledge,  to  confine  this  grading 
to  very  narrow  limits.  The  above  suggestion  may  be  used 
until  future  investigation  finds  a  better.  New  Jersey,  whose 
gravel  roads  are  considered  to  be  exceptionally  good,  and  several 
other  States,  have  begun  a  scientific  grading  of  gravel.  The 
1915  New  Jersey  Specifications  for  the  construction  of  gravel 
roads  are  as  follows : 

Road  Gravel. — Road  gravel  shall  be  composed  of  quartz  pebbles,  sand, 
clay  and  oxide  of  iron  in  such  quantities  that  the  gravel  will  compact  under 
pressure  into  a  hard,  dense  pavement.  It  must  not  contain  over  5  per  cent 

1  Transactions  of  the  American  Society  of  Civil  Engineers,  Vol.  59,  '07. 


172  GRAVEL  ROADS 

of  material  retained  on  l|-inch  circular  openings  nor  over  35  per  cent 
material  retained  on  £-inch  circular  openings. 

Road  gravels  shall  be  divided  into  three  grades,  as  follows:  Grade  A 
is  a  pebbly  gravel,  the  binder  in  which  is  clay.  Grade  B  is  a  sandy,  fer- 
ruginous gravel  depending  upon  the  oxide  of  iron  for  its  cementing  prop- 
erties. Grade  C  is  a  gravel  which  does  not  meet  the  requirements  speci- 
fied in  Grades  A  or  B,  but  may,  on  approval  by  the  engineer  and  the  State 
Commissioner  of  Public  Roads  be  used  for  foundation  of  gravel  roads. 
All  gravel  for  road  work  must,  in  addition  to  the  above  requirements, 
fulfill  the  additional  requirement  given  below. 

Grade  A  must  be  within  the  following  limits  of  composition :  Materials 
retained  on  |-inch  circular  openings,  not  less  than  25  per  cent,  or  over  35 
per  cent;  total  material  retained  on  a  10-mesh  sieve,  not  less  than  40  per 
cent  or  over  60  per  cent;  material  passing  a  200-mesh  sieve,  not  less  than  8 
per  cent  or  over  20  per  cent;  balance  of  the  material  to  be  sand  fairly  well 
graded  and  sharp. 

Grade  B  must  not  contain  less  than  20  per  cent  or  over  40  per  cent  of 
material  retained  on  a  10-mesh  sieve,  nor  less  than  10  per  cent  of  material 
or  over  25  per  cent  of  material  passing  a  200-mesh  sieve.  Of  the  material 
passing  a  200-mesh  sieve,  at  least  40  per  cent  must  be  soluble  in  dilute 
hydrochloric  acid,  1:3. 

The  Colorado  Specifications  contain  this  stipulation  relative 
to  sizes: 

The  gravel  may  be  pit,  bank  or  river  gravel,  and  may  be  taken  from' 
the  pit  or  run  through  the  crusher,  but  at  least  60  per  cent  must  be  of  such 
sizes  as  will  pass  a  2^ -inch  screen  and  be  retained  on  a  |-inch  screen.  The 
test  for  this  quality  to  be  made  by  shoveling  against  a  screen  inclined  45° 
to  the  horizontal. 

The  Missouri  specifications  require  the  gravel  of  the  first 
course  to  be  not  less  than  2  inches  and  not  more  than  4  inches 
measured  on  .the  greatest  diagonal.  For  the  second  course  not 
less  than  ^  inch  nor  larger  than  2  inches  and  "  shall  contain  not 
more  than  30  per  cent  of  material  of  less  dimensions." 

In  the  American  Society  of  Municipal  Improvements  speci- 
fications (1916)  is  found  this  stipulation: 

Sizes  of  Gravel  Mixtures. — Two  mixtures  of  gravel,  sand  and  clay  shall 
be  used  .  .  .  designated  ...  as  No.  1  product  and  No.  2  product. 

No.  1  product  shall  consist  of  a  mixture  of  gravel,  sand  and  clay,  with 
proportions  of  the  various  sizes  as  follows :  All  to  pass  a  1  ^-inch  screen  and 
to  have  at  least  60  and  not  more  than  75  per  cent  retained  on  a  |-inch 


STANDARDIZING   THE   GRADING  173 

screen ;  at  least  25  and  not  more  than  75  per  cent  of  the  total  coarse  aggre- 
gate, material  over  j  inch  in  size,  to  be  retained  on  a  f-inch  screen;  at 
least  05  arid  not  more  than  85  per  cent  of  the  total  fine  aggregate,  material 
under  ^-inch  in  size,  to  be  retained  on  a  200-mesh  sieve. 

No.  2  product  shall  consist  of  a  mixture  of  gravel,  sand  and  clay  with 
the  proportions  of  the  various  sizes  as  follows:  All  to  pass  a  2^-inch  screen 
and  to  have  at  least  60  and  not  more  than  75  per  cent  retained  on  a  j-inch 
screen ;  at  least  25  and  not  more  than  75  per  cent  of  the  total  coarse  aggre- 
gate to  be  retained  on  a  1-inch  screen;  at  least  65  and  not  more  than 
85  per  cent  of  the  total  fine  aggregate  to  be  retained  on  a  200-mesh  sieve. 

ADOPTING  AND  PLOTTING  A  STANDARD  GRADING 

While  it  is  not  necessary,  in  order  to  secure  good  gravel 
roads,  to  grade  the  material  mechanically  so  as  to  produce  a 
maximum  density,  there  is  no  doubt  but  that  such  grading  will 
hasten  consolidation  and  retard  raveling.  It  would  seem  as 
though  five  test  sieves  could  be  used  for  laboratory  examina- 
tions in  nearly  every  case  without  much  trouble: 

The  finest,  either  200  or  100-mesh. 

The  10-mesh. 

The  coarsest. 

The  one  separating  about  35  per  cent  of  the  adopted 

standard. 
The  one  separating  about  65  per  cent  of  the  adopted 

standard. 

In  analyzing  gravel,  the  coarsest  sieve  would  probably  be 
first  used,  and  what  passes  placed  on  the  next  coarsest,  and 
so  on.  The  10-mesh.  separates  what  has  arbitrarily  been 
denominated  the  sand  from  the  gravel,  and  the  200-mesh,  the 
clay  from  the  sand,  the  other  two  separations  determine  whether 
or  not  the  gravel  is  a  graded  mixture. 

Having  adopted  a  standard  mixture,  the  curve  may  be 
plotted  by  the  author's  straight-line  method  and  combinations 
made  up  from  different  pits  as  in  the  sand-clay  road  surface.1 
The  advantages  of  plotting  the  standard  curve  as  a  straight 
line  are :  First,  Ease  of  plotting,  as  any  sheet  of  paper  ruled  one 

1  For  method  of  plotting  straight-line  curves,  see  Chapter  VII,  p.  154. 


174  GRAVEL  ROADS 

way  may  be  used;  second,  the  ordinates  representing  the  finer 
sieves  are  spaced  farther  apart,  thus  magnifying  and  making 
more  distinct  that  portion  of  the  curve;  third,  it  is  easy  to 
compare  any  other  grading  with  the  straight-line  grading. 

Selecting  Gravel. — Besides  the  sieve  analysis,  the  common 
method  of  determining  suitability  of  a  gravel  for  road  purposes 
is  to  note  its  action  in  and  about  the  pit.  If  it  is  packed  firmly 
in  the  pit  and  stands  in  almost  perpendicular  walls,  it  probably 
will  bind  well  on  the  road.  Cementing  tests  such  as  for  mac- 
adam stone,  page  184,  should  be  made  on  each  variety  of  gravel. 
The  American  Society  for  Municipal  Improvements  requires  a 
cementation  coefficient  of  50. 

Chemical  tests  will  determine  the  character  of  the  binding 
impurities  found  in  the  gravel.  A  mineralogical  analysis  will 
answer  as  well  and  is  much  easier  made.  Iron  oxide  often 
found  with  gravel  and  clay,  makes  an  excellent  binder.  A 
ball  of  the  fine  materials  may  be  formed,  dried,  and  roasted  in 
the  furnace.  If  iron  oxide  is  present  the  roasted  product  will 
show  the  characteristic  brick  red  color. 

The  binding  action  may  be  and  probably  is  both  mechanical 
and  chemical.  The  mechanical  action  is  greatest  when  the 
stone  is  so  graded  that  the  voids  of  the  larger  particles  are  filled 
with  smaller  particles  and  the  voids  of  the  smaller  by  still  smaller. 
The  grading  should,  therefore,  be  such  that  a  minimum  of  the 
impalpable  dust  is  required.  The  extremely  fine  dust  when 
subjected  to  moisture  and  pressure  produces  a  weak  cement. 
The  cementing  property  may  be  due  to  chemical  action.  Some 
stones  show  this  property  very  much  more  than  others.  Peb- 
bles of  bluish  color  usually  cement  together  better  than  those  of 
a  reddish  or  brown  color,  hence  the  well-known  superiority  of 
"blue  gravel  "  for  road  purposes.  Trap  rock  gravels  possess 
the  property  of  cementation  to  a  high  degree;  limestone  to  a  fair 
degree;  quartz  wears  well  and  is  tough  but  has  a  small  degree  of 
cementation.  Mica  produces  a  lubricating  effect  and  is,  there- 
fore, detrimental  to  road  gravel.  Gravels  lacking  in  binding 
qualities  may  be  improved  by  mixing  with  clay,  marl,  iron 
oxide,  limestone,  or  trap-rock  dust. 


GRAVEL  ROAD   CONSTRUCTION 


175 


CONSTRUCTION 

Drainage. — The  sub-grade  for  a  gravel  road  should  be  pre- 
pared in  the  same  manner  as  that  described  for  earth  roads. 
Drainage  is  just  as  important  with  a  gravel  wearing  surface,  as 
without  it.  A  dry  cellar  is  necessary,  if  the  roof  is  to  be  kept 
tight  and  in  form.  Furthermore,  the  thickness  of  the  layer  of 
gravel  necessary  for  success  diminishes  with  the  degree  of  drain- 


Plan 


18  teeth  1  sq.  x  16  Ig.  made  of  6.5  %    carbon  steel 
2  -  3x  6  bolted 

HM*n  !!.  jSo   j!.   j!     j! 


II     I     II     tt     II 


Elevation 

FIG.  98. — Harrow  for  Smoothing  Gravel  Roads 

age.  Where  gravel  is  scarce  it  is,  therefore,  economy  to  look 
well  to  the  drainage.  With  an  extremely  thick  layer  of  gravel 
the  under  portion  acts  as  a  drainage  system. 

Design. — There  are  two  methods  of  construction  which  are 
termed  the  surface  method  and  the  trench  method.  With 
either  method  the  gravel  may  be  deposited  in  one  or  several 
layers.  Likewise  the  loose  method,  leaving  the  consolidation 
of  the  material  to  traffic,  or  the  compressed  method,  where  a 
roller  is  used  for  the  compacting,  may  be  employed,  the  former 
to  be  used  only  as  a  last  expedient. 
t 


176  GRAVEL  ROADS 

Surface  Method. — The  gravel  is  dumped  upon  a  properly 
shaped  sub-grade  and  spread  with  shovels  and  rakes.  A  heavy 
A-shaped  l  tooth-harrow  will  aid  in  distributing  and  mixing  the 
gravel,  also,  a  scraping  grader  will  be  found  advantageous  for 
spreading  it 

This  gravel  by  the  loose  method,  which  is  not  recommended, 
is  spread  only  3  or  4  inches  deep  and  allowed  to  be  consolidated 
by  the  traffic.  Then  another  layer  placed  upon  it  and  packed 
in  the  same  manner,  and  this  process  continued  until  the 
required  thickness  is  obtained.  From  time  to  time  after  rains 
while  this  is  going  on  the  road  should  be  shaped  and  smoothed 
by  the  King  road  drag. 

With  the  compressed  method  after  harrowing  and  shaping 
a  roller  is  placed  upon  the  road  and  the  rolling  continued  until  a 
firm  surface  is  produced.  During  the  last  of  the  rolling  the 
surface  should  be  sprinkled  with  water  to  assist  with  the  com- 
pacting. Most  road  men  prefer  to  have  the  gravel  deposited  in 
comparatively  thin  layers  so  that  it  is  compacted  from  the 

1  Fig.  98  shows  a  spike-tooth  harrow  used  by  the  Utah  Highway  Com- 
mission, who  give  the  following  method  for  its  use: 

"The  method  of  harrowing  ordinarily  used  is,  briefly,  as  follows: 
After  the  gravel  is  dumped  in  the  sub-grade,  it  is  spread  with  shovels  and 
stone  rakes  having  the  tines  about  1£  inch  apart  or  with  a  road  machine. 
Stones  which  the  rake  collects  are  pulled  forward  onto  the  earth  sub- 
grade.  After  spreading  the  harrow  is  dragged  over  the  loose  gravel  until 
a  uniform  mixture  is  obtained.  As  a  rule,  four  or  five  trips  are  sufficient 
to  accomplish  this.  If  the  road  is  narrow  teams  may  be  hitched  so  they 
can  walk  on  the  earth  shoulders,  which  is  an  advantage.  When  gravel  is 
laid  in  two  courses  the  top  course  should  receive  the  more  thorough  har- 
rowing. Great  care  should  be  used  to  rake  all  over-sized  stones  out  of  this 
course.  This  is  best  accomplished  while  the  harrow  is  in  operation. 

"  In  incorporating  clay  or  loam  binder  in  a  sandy  gravel,  great  care 
should  be  observed  to  see  that  the  binder  is  in  a  dry  and  thoroughly  pul- 
verized condition.  Damp  clay  cannot  be  harrowed  in  without  leaving 
lumps  to  cause  trouble  in  the  future.  Binder  is  best  spread  with  shovels 
from  a  wagon  or  piles  at  the  side  of  the  road.  It  should  never  be  dumped 
on  the  gravel.  An  even  coat  from  j  to  £  inch  thick  should  be  spread 
uniformly  and  the  spike-tooth  harrow  used  to  mix  it  with  gravel  below. 
The  quantity  of  binder  is  dependent  upon  the  condition  of  the  gravel  and 
is  best  determined  by  trial  on  a  short  section  of  road." 


SURFACE  AND  TRENCH   METHODS 


177 


bottom  up  and  equally  dense  throughout.     Figs.  99  and  100 
show  typical  gravel  road  cross-sections. 

Trench  Method. — The  subgrade  is  prepared  in  the  usual 
manner  and  a  trench  is  made  along  the  roadway  as  wide  and 
deep  as  the  graveled  wearing  surface  is  desired.  A  shoulder  of 
earth  at  least  3  feet  wide  is  left  outside  the  trench  to  assist  in 
retaining  the  gravel  in  place.  A  layer  of  gravel  3  or  4  inches 
thick  is  placed  in  the  trench  and  rolled.  It  is  important  that 

Typical  Cross-Sections 
Alabama 
20'  0- J 


FIG.  99. — Typical  Cross-sections  for  Gravel  Roads. 

the  rolling  should  begin  at  the  earth  shoulders,  which  are  first 
rolled  and  the  roller  gradually  worked  toward  the  center.  A 
second  layer  is  placed  in  the  trench  and  the  process  repeated 
until  the  proper  thickness  has  been  obtained.  During  the 
latter  part  of  the  rolling  a  plentiful  supply  of  water  should 
be  sprinkled  on  the  roadway  to  assist  with  the  consolidation.  If 
this  cannot  be  done  rolling  after  a  rain  will  answer. 

Chert  or  Flint. — Chert,  a  non-crystalline  variety  of  quartz 
which  usually  occurs  in  irregularly  shaped  concretions  in  lime- 
stone, is  of  a  flinty  structure,  found  in  both  dark  and  light  colors 


178 


GRAVEL  ROADS 


and  breaks  with  a  conchoidal  fracture.  Where  the  original 
rockbed  has  been  broken  down,  the  chert  nodules  often  remain 
as  beds  of  gravel.  It  is  usually  much  more  angular  than  ordinary 
gravel.  Bank  chert  may  be  quarried  by  blasting,  then  broken 
into  smaller  fragments  by  the  hammer  or  crusher.  Creek  chert 
being  washed  and  cleaned  by  the  washing  and  grinding  action  of 
the  water  usually  contains  less  binding  matter  than  the  bank 
cherts.  Where  insufficient  binder  is  present  the  usual  binders, 
sand  and  clay,  should  be  added.  The  flint  tailings  or  chats 


FIG.  99a.— Spreading  Gravel  with  a  Blade  Scraper.    Courtesy  of  Iowa 
State  Highway  Commission. 

from  the  zinc  mills  of  southern  Missouri  are  of  this  same  char- 
acter. Chert  is  found  in  the  southern  Appalachian  region, 
southern  Illinois,  Missouri,  Arkansas,  Oklahoma,  Kansas, 
and  Nebraska.  Excellent  roads  have  been  constructed  of  this 
material.  The  Office  of  Public  Roads  directed  the  construc- 
tion of  a  road  having  creek  chert  as  a  foundation  and  bank 
chert  for  the  wearing  course  that  after  four  years'  use  was 
said  to  be  in  first-class  condition  although  it  had  not  been 
resurfaced. 


REPAIRS  AND   MAINTENANCE 


179 


REPAIRS  AND  MAINTENANCE 

The  repair  and  maintenance  of  a  gravel  road  is  somewhat 
like  that  of  an  earth  road.     If  the  gravel  surface  has  rutted 


FIG.  100. — Typical  Gravel  Road  Cross-sections 

badly  or  has  worn  thin  it  should  be  picked  up,  plowed  up,  or 
loosened  with  a  scarifier.     The  best  method  to  use  will  depend 


180  GRAVEL  ROADS 

upon  the  amount  to  be  done  and  the  tools  at  hand.  After  the 
surface  has  been  loosened  the  stones  should  be  raked  or  har- 
rowed to  allow  the  fine  dirt  to  settle  to  the  bottom.  New 
gravel  should  then  be  placed  upon  the  road  spread  and  rolled  to 
place.  Before  rolling,  however,  to  save  waste,  the  earth 
shoulders  must  be  put  in  good  condition. 

The  ordinary  maintenance  consists  of  filling  pot  holes  and 
incipient  ruts  by  sweeping,  raking,  or  dragging.  Sometimes  a 
blade  grader  can  be  used  to  advantage.  Steel  drags,  or  drags 
shod  with  steel  are  best  for  use  on  gravel.  Piles  of  gravel  placed 
at  short  distances  along  the  roadway  are  extremely  convenient 
and  allow  the  patrolman  to  make  small  repairs  before  raveling 
takes  place.  After  a  rain  is  an  excellent  time  to  mark  the  spots 
that  should  receive  attention. 


CHAPTER  IX 
BROKEN-STONE  ROADS 

UNTIL  the  advent  -of  the  automobile,  broken-stone  roads 
were  thought  to  be  the  best  type  of  so-called  "  permanent 
roads  "  for  rural  communities.  The  surface  of  such  roads  are 
of  natural  broken  stone  of  varying  sizes  wedged  firmly  together 
by  rolling  and  further  "  bound  "  or  cemented  by  a  weak  cement, 
composed  of  the  dust  worn  from  the  stones  themselves  in  the 
process  of  rolling  or  by  traffic,  and  water.  Such  a  surface  is 
generally  spoken  of  as  "  water  bound."  Dust  and  moisture 
are  essential  elements  in  its  life.  For  greatest  durability,  these 
must  be  in  exactly  right  proportions.  A  road  under  heavy 
traffic  should  have  an  extremely  hard,  tough  stone  while"  one 
under  light  traffic  will  be  best  with  a  softer  and  more  friable 
stone. 

The  quality  of  stone  for  road  purposes  may  be  tested  by  the 
methods  and  machines  adopted  by  the  U.  S.  Office  of  Public 
Roads,  a  brief  synopsis  of  which  is  given  here. 

TESTING  ROAD  STONE  l 

The  chief  properties  essential  to  good  road  materials  are 
hardness,  toughness,  and  cementing  or  binding  power. 

Hardness. — The  test  is  known  as  the  Dorry  test  and  con- 
sists in  grinding  specimens  with  sand  of  a  standard  size  and 
quality.  Hardness  thus  found  may  be  defined  as  the  resistance 
which  a  material  offers  to  the  displacement  of  its  particles  by 
friction.  The  measure  is  inversely  as  the  loss  of  weight  arising 
from  the  scoring  by  an  abrasive  agent. 

1  Bulletin  No.  79.  U.  S.  Office  of  Public  Roads.  See,  also,  Bulletins 
28,  31,  and  44. 

181 


182 


BROKE-NSTONE  ROADS 


Fig.  101  shows  the  Dorry  machine.  It  consists  of  a  revolving 
steel  disk  upon  which  is  pressed  by  constant  weights  of  1250 
grams,  two  small  stone  cylinders  25  millimeters  (1  inch)  in 
diameter  and  25  millimeters  long.  Upon  the  cylinder  as  it 
revolves  is  spread  standard  quartz  sand  which  will  pass  a  30- 
and  be  retained  on  a  40-mesh  sieve.  The  test  piece  is  made  true 


FIG.  101. — Dorry  Hardness  Testing  Machine. 


to  shape  then  weighed  and  ground  on  one  face  for  1000  revolu- 
tions; it  is  then  turned  over  and  ground  on  the  other  face  for 
1000  revolutions.  The  loss  in  weight  is  found  after  each  1000 
revolutions  and-  the  average  is  used  in  stating  the  hardness 
which  is  expressed  by  the  formula 

Hardness  =  20  -JTF, 


TESTS   FOR   HARDNESS.   TOUGHNESS 


183 


where  W=loss  in  grams  per  1000  revolutions.     Stone  having  a 

coefficient  in  hardness  below  14  is  called  soft,  14  to  17  medium 

and  above  17  hard. 

Toughness  may  be  defined  as  the  resistance  a  rock  offers 

to  fracture  under  impact,  such  as  the  blow  of  a  hammer;  it  is 
the  opposite  of  brittleness  and  fri- 
ability. It  is  tested  by  the  machine 
shown  in  Fig.  102,  which  is  essentially  a 
small  pile  driver.  A  2-kilogram  weight 
falling  a  distance  of  1  centimeter  for 
the  first  blow,  2  centimeters  for  the 
second  blow  and*  increasing  1  centi- 
meter for  each  blow  until  fracture 
occurs.  The  test  piece  is  like  that 
used  in  the  Dorry  machine,  a  cylinder 


FIG.  102. 


FIG.  103. 


Photographs  of  a  Page  Impact  Machine  and  of  a  Ball  Mill  in  the  Road 
Laboratory  of  the  University  of  Nebraska. 

(25  cm.  in  diameter)  drilled  with  a  core  drill  from  the  solid  rock 
and  faced  off  25  cm.  long.  The  number  of  blows  which  is  the 
height  of  fall  of  the  last  blow  in  centimeters,  is  the  measure 
of  toughness.  Rocks  testing  below  13  are  low;  from  13  to  19, 
medium;  above  19,  high. 


.184  BROKEN-STONE   ROADS 

Cementing  Value. — This  is  defined  as  the  binding  power  of 
the  road  material  and  the  test  for  it  is  made  as  follows:  Five 
hundred  grams  of  the  rock  to  be  tested  are  ground  in  the  ball 
mill,  Fig.  103,  with  sufficient  water  to  form  a  dense  fine-grained 
paste.  The  ball  mill  is  a  hollow  casting  in  which  roll  two 
chilled  steel  balls  which  weigh  25  pounds  each  and  is  revolved 
about  2000  revolutions  per  hour.  The  thoroughly  kneaded 
paste  or  dough  is  removed  and  placed  in  a  metal  die,  25  mm.  in 
diameter  and  subjected  to  a  pressure  of  132  kilos  per  square 
centimeter.  The  pressure  is  gradually  applied  until  a  weight 


FIG.  104. — Photograph  of  a  Page  Impact  Machine,  for  Testing  Cementing 
Value,  in  the  Road  Laboratory  of  the  University  of  Nebraska. 

at  the  end  of  a  lever  is  raised  and  it  is  then  immediately  released. 
The  amount  of  paste  used  is  just  sufficient  to  form  a  cylinder 
25  mm.  long.  Five  briquettes  are  made  and  allowed  to  dry 
in  air  one  day  and  in  a  hot  oven  at  200°  F.  for  four  hours,  then 
cooled  in  a  desiccator  for  twenty  minutes.  The  briquettes 
after  drying  are  tested  in  the  machine  shown  in  Fig.  104.  A 
1 -kilogram  hammer  is  raised  by  a  cam  and  allowed  to  drop  on 
plunger  which  transmits  the  impact  to  the  test-piece.  The 
instrument  has  a  cylinder  about  which  is  wound  a  strip  of  sili- 
cated  paper  and  on  which  is  automatically  recorded  the  number 
of  blows  struck  to  produce  fracture,  and  the  resilience  of  the 


CEMENTATION   AND   ABRASION   TESTS  185 

test  piece.  The  average  number  of  blows  on  the  five  briquettes 
is  taken  as  the  result  of  the  test.  A  result  of  10  is  low,  10  to 
25  fair,  26  to  75  good,  76  to  100  very  good,  over  100  excellent. 
In  making  this  test  care  must  be  taken  that  the  dough  in  the 
ball  mill  has  become  thoroughly  pulverized  and  kneaded. 

Resistance  to  wear,  although  depending  largely  upon 
hardness  and  toughness,  is  a  special  property  which  cannot  be 
exactly  determined  as  a  function  of  these.  The  method  of 


FIG.  105. — Deval  Abrasion  Machine. 

testing  for  it  was  devised  by  the  French  and  is  done  by  means 
of  the  Deval  abrasion  machine,  Fig.  105.  The  ma«hine  con- 
sists of  one  or  more  hollow  iron  cylinders  mounted  on  a  shaft 
so  that  the  axes  of  the  cylinders  make  an  angle  of  30°  with  the 
shaft.  As  the  shaft  is  revolved  the  rock  in  the  cylinders  is 
thrown  from  one  end  to  the  other.  The  impact  and  abrasive 
action  together  tend  to  break  the  pieces  of  rock  into  finer  and 
finer  particles.  The  rock  to  be  tested  is  broken  into  pieces  from 
1£  to  2|  inches  in  size.  Five  kilograms  (within  10  grams) 


186  BROKEN-STONE  ROADS 

fifty  pieces  if  possible,  are  placed  in  the  diagonally  mounted 
cast-iron  cylinder  and  slowly  revolved  10,000  times  at  a  rate 
between  30  and  33  revolutions  per  minute.  The  material  worn 
off  which  will  pass  a  r^-inch  mesh  sieve  is  considered  the 
amount  of  wear.  This  is  expressed  either  as  a  percentage  of 
the  charge  (5  kilograms)  or  by  the  French  coefficient  of  wear  — 

20_400 
KW~  W 

W  being  the  weight  in  grams  of  the  detritus  under  TG  inch  in 
size  —  per  kilogram  of  rock  used.  The  French  engineers  who 
were  the  first  to  undertake  the  testing  of  road  materials  divided 
40  by  the  percentage  of  wear  in  order  that  a  higher  coefficient 
might  show  a  better  rock  than  a  lower  coefficient.  They  found 
that  their  best-wearing  rocks  gave  a  coefficient  of  about  20. 
The  number  20  was,  therefore,  adopted  as  a  standard  of  excel- 
lence. A  coefficient  of  8  is  low;  8  to  13,  medium;  14  to  20, 
high;  above  20,  very  high. 

These  are  the  principal  tests  used.  Other  tests  may  be 
made,  thus: 

Specific  gravity  is  determined  by  weighing  a  rock  in  air  and 
in  water  and  dividing  the  weight  in  air  by  the  loss  of  weight  in 
water.  If  W  =  weight  in  air,  and  w  =  weight  in  water 


The  specific  gravity  multiplied  by  62J  gives  the  weight  of  the 
rock  substance  per  cubic  foot. 

Apparent  Specific  Gravity,  A.  S.  T.  M.  Standard.1 

^ 

Apparent  Specific  Gravity  =  TT^TJ, 

where  A  —  weight  of  sample,  dried  to  constant  weight  at  a 
temperature  between  100  and  110°  C.,  should  be 
within  .5  gram  of  1000  grams,  composed  of  pieces 
aproximately  cubical  or  spherical  which  will  be 
retained  on  a  J-inch  screen; 
1  1918  Standards,  p.  628. 


SPECIFIC   GRAVITY.    ABSORPTION  187 

B  =  weight  of  sample  after  having  been  soaked  in  water 
for  twenty-four  hours,  the  surface  water  absorbed 
by  a  blotting  paper  or  a  towel; 

C  =  weight  of  sample  suspended  in  water  from  the  center 
of  a  scale  pan  in  a  wire  basket  less  the  weight  of 
the  basket  suspended  in  water,  that  is,  the  weight 
of  the  saturated  sample  immersed  in  water. 

Absorption. — The  amount  of  water  which  a  rock  will  absorb 
is  sometimes  taken  to  measure  durability.  The  idea  being,  the 
more  water  absorbed,  the  more  effect  freezing  will  have  on  the 
rock.  This  does  not  always  follow. 

Compression. — High  compressive  tests  usually  mean  good 
quality  of  stone  for  building  purposes  but  not  necessarily  for 
road  purposes;  however,  this  property  taken  in  combination 
with  the  other  tests  is  of  value. 

Simpler  Methods  of  Judging  the  Character  of  the  Rock. — 
The  durability  of  a  rock  under  the  action  of  the  weather  may 
be  judged  by  the  character  of  the  outcropping  of  the  ledge  at 
the  ground  surface  or  by  stones  which  have  lain  out  for  a 
number  of  years.  If  these  show  a  decided  tendency  to  disin- 
tegrate, they  will  probably  do  the  same  in  the  road.  The 
toughness  and  hardness  may  be  judged  by  breaking  wfrh  a 
hammer.  Easily  broken  brittle  stones  lack  toughness.  The 
effect  of  the  hammer  upon  the  appearance  of  a  freshly  fractured 
surface  will  furnish  a  general  estimate  of  resistance  to  wear  and 
specific  gravity.  But  after  all  the  best  test  is  the  behavior  of  the 
stone  in  the  road  itself  or  in  roads  of  a  similar  character. 

CLASSIFICATION  OF  ROCKS 

The  U.  S.  Office  of  Public  Roads  has  divided  rocks  for  road- 
making  purposes  into  three  classes  and  these  are  again  divided 
into  Types  and  Families  as  shown  by  the  following  table,  taken 
from  Bulletin  31,  by  Edwin  C.  E.  Lord: 

With  the  exception  of  rocks  of  the  second  class,  where 
chemical  distinctions  prevail,  structural  features  indicating 


188  BROKEN-STONE   ROADS 

TABLE     I.— GENERAL    CLASSIFICATION     OF     ROCKfe 


Class 


Type 


Family 


I.  Igneous 


II.  Sedimentary. . . 


III.  Metamorphic . 


1.  Intrusive  (plutonic) 


2.  Extrusive(Volcanic) 


f  1.  Calcareous 


2.  Siliceous 


1.  Foliated 


2.  Non-foliated 


a.  Granite 

6.  Syenite 

c.  Diorite 

d.  Gabbro 

e.  Peridotite 

a.  Rhyolite 
6.  Trachyte 

c.  Andesite 

d.  Basalt  and  diabase 

a.  Limestone 

b.  Dolomite 

a.  Shale 

6.  Sandstone 

c.  Chert  (flint) 

a.  Gneiss 
6.  Schist 
c.  Amphibolite 

a.  Slate 

6.  Quartzite 

c.  Eclogite 

d.  Marble 


mode  of  origin  define  a  type,  and  mineral  composition  the 
family. 

Igneous  Rocks  are  those  which  are  formed  by  solidification 
from  a  molten  state  either  beneath  the  surface  of  the  earth 
(intrusive)  or  upon  reaching  the  surface  (extrusive).  Miner- 
alogically  some  of  the  intrusive  rocks  may  be  the  same  as  the 
extrusive,  they  will,  however,  differ  in  structure. 

Sedimentary  or  Aqueous  Rocks  are  the  consolidatec^product 
of  former  rock  disintegration  or  they  have  been  formed  from 


CLASSIFICATION  OF  ROAD   ROCKS  189 

the  accumulation  of  organic  remains.  These  materials  have 
been  transported  by  water  and  deposited  in  layers  giving  the 
characteristic  stratified  structure. 

Metamorphic  Rocks  are  those  which  have  undergone  change 
due  to  prolonged  action  of  physical  and  chemical  forces  such  as 
heat,  pressure,  moisture  and  various  attending  chemical  agen- 
cies. 

MINERAL  COMPOSITION 

Rocks,  as  ordinarily  known,  are  combinations  of  minerals. 
Quartz,  which  is  almost  pure  silica,  is  the  most  common.  Ortho- 
clase  (silicate  of  alumina  and  potash)  and  plagioclase  (silicate 
of  alumina,  lime,  and  soda)  are  prominent  minerals  in  the 
feldspars  or  field  stones  and  hence  in  road-making  rocks.  Other 
minerals  of  common  occurrence  are  augite,  hornblende,  calcite, 
dolomite,  and  bistite.  A  number  of  others  formed  largely  by 
decomposition  of  primary  minerals  furnish  valuable  cementing 
properties  to  road  rock;  for,  example,  chlorite,  kaolin,  epidote, 
calcite,  and  limonite. 

PRINCIPAL  ROAD  ROCKS 

Trap  rocks  have  long  been  known  to  form  the  best  road 
stone.  These  are  finely  crystalline  igneous  formations,  and 
usually  of  a  dark  color,.  Many  of  them  in  cooling  run  over 
each  other  in  broad  steps  or  trappa  (Swedish  for  stair)  hence  the 
name  trap.  The  principal  mineral  constituent  is  plagioclase. 
Included  among  them  and  largely  used  for  road  purposes  are: 

Basalt,  a  glassy-porphyritic  homogeneous  rock  of  dark  gray 
or  black  color. 

Diabase,  a  holocrystalline  or  granular  rock  of  green  or 
dark  gray  color. 

Peridotite,  variable  in  structure,  either  crystalline,  granular 
or  porphyritic  (a  compact  structure  with  large  crystals)  and 
greenish  or  black  in  color. 

Andesite,  glassy  to  holocrystalline  in  structure  and  varying 
from  a  greenish  to  reddish  color. 

Other  rocks  frequently  used  though  less  durable  are : 


190  BROKEN-STONE   ROADS 

Diorites,  whose  mineral  elements  are  largely  feldspar, 
plagioclase  and  hornblende.  They  are  green,  dark  gray  or 
black  in  color. 

Granites  are  largely  composed  of  quartz,  orthoclase  and 
plagioclase,  combined  with  mica  and  hornblende.  Are  holo- 
crystalline  granular  in  structure. 

Syenites  are  similar  to  granites  except  they  do  not  contain 
quartz. 

Gneisses  have  a  holocrystalline  granular  structure  arranged 
in  parallel  bands. 

CONSTRUCTION  OF  STONE  ROADS 

The  subgrade  of  a  stone  road  should  be  prepared  similar 
to  that  of  an  earth  road.  The  drainage  should  be  carefully 
looked  after,  side  drains  placed  where  necessary  to  lower  the 
ground  water  below  the  frost  line.  Wet  soil  in  freezing, 
"  heaves  "  the  roadway  loosening  the  stones  by  breaking  the 
bond  allowing  the  larger  stones  to  come  to  the  top  where  they 
will  pick  out  under  traffic.  A  wet,  soft  material  in  the  sub- 
grade  will  be  forced  up  into  the  interstices  and  the  surface  will 
become  uneven.  Surface  water  must  be  cared  for  by  side 
ditches  and  suitable  runways,  culverts  and  bridges.  The  sub- 
grade,  if  not  already  compact  under  traffic,  should  be  thoroughly 
rolled  to  prevent  settlement. 

Stone  roads  are  usually  classified  as  telford  and  macadam, 
so  named  after  Telford  and  Macadam,  two  eminent  road 
builders  of  England.1 

1  Thomas  Telford  was  born  in  Dumfriesshire,  Scotland,  August  9,  1757, 
and  died  September  2,  1834.  He  was  one  of  the  greatest  civil  engineers  of 
his  time.  He  constructed  bridges  over  the  Severn,  across  the  Tay  and 
at  numerous  other  places,  planned  and  superintended  the  Ellismere  Canal, 
was  commissioned  by  .the  government  to  report  on  the  public  works  required 
for  Scotland,  constructed  the  Caledonian  Canal,  executed  more  than  1000 
miles  of  roads  in  Scotland  and  England,  and  designed  and  constructed 
harbor  improvements  at  Pullneytown,  Aberdeen,  Dover,  London,  and  many 
other  ports.  He  was  one  of  the  founders  of  the  Institute  of  Civil  Engi- 
neers and  for  many  years  was  president.  He  received  recognition  and 
honor  from  his  home  and  foreign  countries.  For  the  Austrian  government. 


TELFORD  AND   MACADAM   ROADS  191 

Tresaguet  in  France  had  built  roads  previously  and  these  men 
were,  no  doubt,  familiar  with  his  work,  but  the  English-speaking 
nations  have  perpetuated  these  two  names  in  lasting  monu- 
ments by  calling  the  two  principal  classes  of  stone  roads 
"  macadam  "  and  "  telford." 

A  macadam  road  is  one  surfaced  with  small  angular  broken- 
stones  compacted  and  wedged  together  and  further  bound  by 
stone  dust,  all  upon  the  earth  subgrade.  The  broken  stone  is 
frequently  spoken  of  as  macadam.  The  telford  road  is  essen- 
tially the  same  with  this  difference,  the  foundation  is  made  by 
paving  the  earth  subgrade  with  stones  of  a  larger  size  and  then 
upon  this  foundation  placing  the  macadam  surface.  Now- 
adays, roads  over  very  wet  country  adopt  the  telford,  and  those 
on  comparatively  solid  well-drained  ground,  the  macadam 
type,  Fig.  106,  also  see  Fig.  118,  Chapter  X. 

he  built  the  road  from  Warsaw  to  Brest.  Because  of  his  work  on  the 
Gotha  Canal  the  King  of  Sweden  conferred  on  him  an  order  of  knighthood; 
while  at  his  death,  his  own  country  buried  him  in  Westminster  Abbey. 

John  Loudon  Macadam  was  born  at  Ayr,  Scotland,  September  21,  1756, 
and  upon  the  death  of  his  father  in  1770  went  to  live  with  an  uncle  in  New 
York.  He  entered  his  uncle's  counting  house,  became  a  successful  mer- 
chant and  on  returning  to  Scotland  in  1783  bought  an  estate  in  Ayrshire. 
He  was  later  appointed  deputy-lieutenant  for  the  county  and  while  per- 
forming the  duties  of  that  office  became  interested  in  roads.  In  1810  he 
began  experimenting  by  putting  broken  stone  in  the  swampy  roads*.  In 
1816  he  became  inspector  of  the  Bristol  Turnpike  Trust  and  superintended 
the  reconstruction  of  178  miles  of  road.  In  1817  he  built  the  first  mac- 
adam roads  in  London,  where  he  was  appointed  street  commissioner  the 
same  year.  Slowly  the  system  of  road  making  which  he  advocated,  although 
he  may  not  have  been  its  actual  inventor,  spread  throughout  the  empire. 
In  1827  Parliament  appointed  him  Surveyor  General  of  Metropolitan 
Roads'and  voted  him  $48,000.  Three  works  on  the  subject  of  roads  were 
written  by  him.  He  died  November  26,  1836. 

Pierre-Marie  Tresaguet  was  a  noted  French  engineer  born  at  Nevers, 
in  1716,  and  died  at  Paris  in  1796.  He  is  sometimes  called  the  father  of 
modern  road  building,  having  built  stone  roads  before  either  Macadam  or 
Telford.  He  built  roads  on  a  plan  similar  to  that  afterwards  used  by 
Telford  in  Scotland.  He  laid  the  foundation  for  the  splendid  system  of 
roads  in  France  by  recognizing  the  necessity  for  organized  continouus 
maintenance  after  substantial  construction. 


192  BROKEN-STONE  ROADS 

Subgrade. — The  subgrade  is  prepared  for  the  stone  by 
excavating  a  trench  sufficiently  deep  and  wide  for  the  com- 
pacted stone  surface.  The  bottom  of  the  trench  may  be  either 
level,  V-shaped  or  parallel  to  the  finished  surface.  The  level 
surface  is  a  little  easier  to  make,  the  V-shaped  furnishes  addi- 
'tional  drainage  providing  suitable  outlets  are  made  frequently 
along  the  road,  but  the  crowned  ditch  is  the  one  most  usually 
used.  This  makes  the  thickness  of  the  metal  uniform  over  the 
roadway,  thus  saving  in  the  quantity  of  material.  The  earth 


»E®Sgv:  2B5BSB1 

—  15-0 


V  UNDCRDfM/N 

CoU>lf-/i/M  toryrifoflfs  at  bottom,  smo'/stonetoiKffWf'rtfiy* 


hrmy  sab  grmtt  m  ckpltu  varying  ~g.lort;rsrcnrs  ffaffa/Aafft* 
fan  4~A>  10'p/omt  undrr  macadam   VgK  yvo*&  to  fintotfop 
-U™ 

S/D£  DRAIN.  BUND  DMM. 

FIG.  106.  —  Typical  Cross-sections. 

from  the  trench  is  piled  along  the  roadway  and  used  for  the 
shoulders  later,  and  prevents  the  spreading  of  the  macadam 
when  it  is  rolled.  The  bottom  of  the  trench  should  be  rolled 
to  a  firm  true  surface  so  that  under  the  roller  or  traffic  the 
stone  will  not  unduly  cut  into  it  or  the  earth  squeeze  up  into 
the  stone. 

The  cross-sections,  Figs.  106,  107,  all  show  a  certain  amount 
of  crowning.  Three-quarters  of  an  inch  to  the  foot  is  usually 
considered  sufficient  thus,  for  a  roadway  16  feet  wide  the  center 
would  be  raised  6  inches.  On  roads  of  considerable  width,  as, 


STANDARD   SECTIONS 


193 


naturally,  they  will  be  roads  having  heavy  traffic  and  constant 
attention,  the  crown  may  be  reduced  to  \  inch  per  foot.  There 
is  little  difference  whether  the  crown  be  made  of  two  sloping 
planes  with  the  intersection  rounded  or  of  a  parabolic  form. 


SECTION  26 


H~  -  -2HT7 4' 

!-«--6  0--*^    6  0---H**h 1 


S£C7YO/V  27 


SECTION  SO 

FIG.  107. — Standard  Macadam  Sections  for  Illinois  Roads. 

Section  26 — Twelve-foot  water-bound  macadam  roadway  with  earth  shoulders.  To 
be  used  in  a  level  country.  Section  27 — Twelve-foot  water  bound  macadam  roadway 
with  earth  shoulders  and  broad  side  ditches  available  for  traffic  where  width  between 
fences  permits.  Especially  adaptable  for  a  low-lying  level  country.  Section  28 — 
Twelve-foot  water-bound  macadam  roadway  with  earth  shoulders.  To  be  used  on  deep 
fills.  For  shallow  fills  use  Section  1.  Section  29 — Twelve-foot  water-bound  macadam 
roadway  for  single  track  roads  in  deep  cuts  on  grades  that  require  grouted  gutters. 
Section  30 — Twelve-foot  water-bound  macadam  roadway  for  single-track  roads  on  deep 
fills  where  grouted  gutters  are  necessary. 

Courses. — Since  it  is  difficult  to  compact  a  layer  of  stone 
more  than  6  inches  thick  stone  roads  are  best  made  in  courses 
having  the  larger  stones  in  the .  lower  course.  This  insures 


194 


BROKEN-STONE  ROADS 


better  under-drainage  and  a  smoother  wearing  surface,  although 
many  stone  roads  have  been  made  with  crusher-run  stone. 
The  voids  between  loosely  spread  broken  stone  amounts  to 
about  40  or  50  per  cent  of  the  volume  of  the  layer  or  course. 
In  the  process  of  rolling  this  is  frequently  reduced  to  30  or  35 
per  cent.  Therefore,  the  loose  layer  should  be  made  about  40 
per  cent  thicker  than  the  compacted  layer  is  desired.  This  is 
a  rough  estimate  for  calculating  quantity  of  stone  required. 
Trial  upon  the  road  is  necessary  for  any  particular  location. 
At  some  places  stones  will  sink  more  into  the  subgrade  than  at 
others;  some  rocks  will  pack  better  than  others.  Table  II 
shows  roughly  thicknesses  of  macadam  required: 

TABLE  I 


LOWER  COURSE 

MIDDLE  COURSE 

UPPER  COURSE 

TOTAL  THICKNESS 

Before 

After 

Before 

After 

Before 

After 

Before 

After 

Rolling 

Rolling 

Rolling 

Rolling 

Rolling 

Rolling 

Rolling 

Rolling 

Si 

2| 

2 

U 

51 

4 

4 

3 

3 

2 

7 

5 

« 

4 

3 

3 

8£ 

6 

51 

4 

4 

3 

9| 

7 

5* 

4 

3£ 

2£ 

2 

« 

11 

8 

5* 

4 

4 

3 

3 

2 

12f 

9 

5* 

4 

tt 

4 

3 

2 

14 

10 

In  addition  to  the  stone  shown  in  the  table  there  will  have 
to  be  provided  the  "  binder,"  which  consists  of  stone  dust 
and  small  fragments  which  will  pass  a  J-inch  screen. 

Placing  the  Broken  Stone. — The  lower  course,  consisting  of 
the  larger  stones — 1 J  to  2J  inches  x  in  diameter — are  spread  first, 
Figs.  108,  109,  HO.2  Unless  self -spreading  wagons  are  used 

1  In  three-course  work  still  larger  stones  should  be  used  in  the  bottom 
course. 

1  From  Bulletin  29,  Office  of  Public  Roads,  U.  S.  Dept.  of  Agriculture. 


PLACING  THE  BROKEN   STONE 


195 


the  stone  should  be  shoveled  from  the  wagons  or  dumped 
directly  on  the  road  and  leveled  the  fragments  appear  to  segre- 
gate and  compact  unevenly;  no  amount  of  rolling  can  remove 
the  hummocks  thus  left. 

After  the  stone  has  been  spread  by  shovels  to  the  required 
depth,  due  allowance  being  made  for  shrinkage,  for  a  hun- 
dred or  so  feet  the  rolling  of  the  first  course  is  begun.  Begin 


FIG.  108.— Placing  the  Stone.     Courtesy  U.  S.  Dept.  of  Agri. 

by  rolling  first  a  part  of  the  earth  shoulder,  working  inward 
toward  the  center  a  few  inches  with  each  round  of  the  roller. 
This  will  prevent  pushing  the  stone  outward.  The  rolling 
should  be  continued  until  the  first  course  is  thoroughly  com- 
pacted and  does  not  wave  before  the  roller.  Sometimes  the 
stone  will  not  pack.  This  may  be  due  to  a  wet  soft  subgrade, 
dry  weather  must  be  waited  for;  it  may  be  the  stone  is  too  hard, 
in  which  case  some  screenings  or  sand  should  be  used ;  the  roller 
may  be  too  heavy,  a  lighter  one  should  be  provided  for  early 


196 


BROKEN-STONE   ROADS 


••BBMHI 


FIG.  109.— Rolling.     Courtesy  U.  S.  Dept.  of  Agri. 


FIG.  110.— Finished  Road.     Courtesy  U.  S.  Dept.  of  Agri. 


CONSTRUCTION  197 

rolling.  Unless  the  stone  is  "  packing  n  continued  rolling  is 
detrimental.  Absolute  rigidity  is  not  necessary  here,  but  a 
firmness  so  the  stones  will  not  heave  before  the  roller  or  quake 
under  the  foot  should  be  obtained. 

If  depressions  occur  they  should  be  filled  with  stone  of  the 
same  size  as  the  course  being  rolled.  When  the  first  course 
is  smooth  and  true  to  cross-section  the  next  course  may  be 
spread. 

Upper  Course. — This  course,  consisting  of  stones  varying 
from  1J  to  1  inch  in  diameter,  is  spread  and  rolled  in  the  same 
manner  as  the  lower  course.  When  the  stones  have  been 
compacted  and  tightly  wedged  together  a  small  layer  of  binder 
is  spread  and  the  rolling  continued  to  force  it  into  the  inter- 
stices. The  watering  cart  is  now  used  and  the  "  fines  "  flushed 
in.  Rolling  is  continued  until  a  wave  of  slush  is  pushed  along 
ahead  of  the  roller.  Only  a  very  little  more  than  enough  "  fines  " 
to  fill  the  interstices  should  be  used.  The  durability  of  the 
road  will  depend  largely  on  the  rigidity  obtained  by  the  wedging 
action  of  the  stones.  Unless  'they  are  held  firmly  in  close  union 
the  weak  cementing  action  of  the  stone-dust  will  be  of  little 
value.  Rolling  is  an  important  operation,  for  not  only  the 
rigidity,  but  the  surface  alignment  and  smoothness,  depend 
upon  the  manner  in  which  it  is  executed. 

Since  the  greater  cementing  action  of  stone-dust  comes  only 
after  the  primary  minerals  have  been  disintegrated  and  the 
secondary  set  up  l  the  true  metallic  ring  of  the  road  will  come 
some  little  time  after  finishing.  Use  of  the  road  as  the  setting 
of  the  cement  takes  place  is  beneficial. 

If  the  subgrade  will  not  harden  sufficiently  resort  should  be 
had  to  tile  or  other  drainage,  or  a  telford  foundation  may  be 
used.  In  Jackson  County,  Mo.,  a  bottom  course  of  native 
limestone  made  up  of  large  stones — "  one-man-size  " — is  used 
as  a  foundation  course,  Fig.  118,  Chapter  X.  A  man  with  a 
sledge  goes  over  this  and  breaks  off  projecting  points  and  the 
whole  is  rolled  to  a  comparatively  smooth  surface  before  the 
macadam  is  laid. 

1  See  Bulletins  28,  31,  85  and  92,  U.  S.  Office  of  Public  Roads. 


198  BROKEN-STONE  ROADS 

Shoulders. — The  earth  thrown  out  of  the  trench  may  be 
smoothed  down  and  will  furnish  either  an  earth  road  along  the 
macadam  or  room  for  turning  out.  Keeping  the  shoulders 
high  and  smooth  will  also  help  to  preserve  the  macadam.  If 
the  earth  sides  are  used  more  or  less  for  traffic  -they  will  remain 
firm  and  the  macadam  will  be  held  in  place.  In  dry  locations 
trees  and  shrubbery  may  be  induced  to  grow  along  the  road- 
way, which,  serving  as  a  wind  break,  will  prevent  the  blowing 
away  of  the  binder.  The  taller  trees,  because  of  their  shade, 
prevent  excessive  drying  out  of  the  road,  besides,  they  are  of 
ornamental  value. 

Width  and  Thickness  of  Macadam.— The  width  cf  the 
macadamized  way  will  depend  upon  local  conditions.  A  one- 
way road  with  good  earth  on  the  side  for  turning  out  may  be  as 
narrow  as  8  feet.  The  general  practice  is  to  build  them  from 
16  to  18  feet  in  width.  Thickness  also  depends  somewhat  on 
traffic  conditions,  4  to  6  inches  after  compaction  is  common. 
A  great  number  of  French  roads  were  measured  and  averaged 
a  little  less  than  5  inches.  Loose  stone  is  estimated  to  con- 
solidate from  J  to  |  under  rolling  and  traffic.  The  table  pre- 
viously given  is  figured  on  approximately  a  30  per  cent  basis. 
Frequently  the  macadam  is  made  thinner  on  the  outer  edges 
than  in  the  center  for  the  reason  that  the  outer  portions  receive 
a  less  share  of  traffic. 

MAINTENANCE 

Continuous  Method. — For  all  classes  of  roads  the  con- 
tinuous method  of  maintenance  is  growing  in  favor.  By  this 
method  a  patrolman  is  kept  on  a  given  section  of  the  road.  He 
watches  for  depressions,  which  show  up  more  clearly  after  a 
rain.  If  the  depression  is  small,  he  may  be  able  to  fill  it  by 
sweeping  into  it  loose  materials  from  the  surrounding  surface 
or  by  bringing  new  material  from  a  pile  near  at  hand.  If  the 
depression  is  larger  and  takes  on  the  nature  of  a  rut  or  chuck 
hole,  it  may  be  necessary  to  pick  up  that  portion  of  the  roadway 
and  apply  new  stone.  The  traffic  will  soon  consolidate  it. 
Dragging  a  macadam  road  with  a  split  log  or  other  drag  will  have 


EFFECT  OF  AUTOMOBILE 


199 


a  tendency  to  fill  depressions  with  detritus  and  leave  the  sur- 
face in  a  smoother  more  acceptable  condition. 

Periodic  Method. — When  the  roadway  has  worn  so  thin  or  it 
has  become  so  rutted  that 
these  methods  are  not  suffi- 
cient,   the    entire    road    is 
picked,    plowed    or    rooted 
up,  the  larger  stones  raked 
or  harrowed  free  from  dirt 
and  dust  and  the  road  re- 
built.    The  picking  may  be          FIG.  111.— Scarifier  or  Rooter, 
done  by  spikes  placed  in  the 

wheels  of  the  roller  or  tractor,  or  it  may  be  done  by  "  scarifiers  " 
or  "  rooters,"  Fig.  Ill,  especially  made  for  that  purpose.  Some- 
times a  mere  resurfacing  of  about  3  inches  of  stone  is  all  that  is 
necessary. 

Effect  of  Automobile  on  Macadam. — One  of  the  worst  foes 


FIG.  112.— (a)  The  Resultant  Pressure  Exerted  by  an  Automobile  Wheel 
upon  the  Road  Surface.  (6)  A  Wedge  of  Earth  Forced  in  by  the 
Resultant  Pressure  Loosening  the  Road  Metal  Back  of  It.  (c)  and 
(d)  Show  How  a  Pencil,  a  Piece  of  Paper  and  a  Weight  on  a  Smooth 
Table  Will  Illustrate  This  Action,  (e)  and  (/)  Show  How  a  Stone 
May  be  Rolled  from  the  Surface  by  the  Backward  Force  of  Friction. 


200 


BROKEN-STONE   ROADS 


of  the  waterbound  macadam  road  is  the  automobile.  The 
power  being  applied  through  the  wheel,  the  resultant  force,  R, 
Fig.  112,  upon  the  road  has  for  components  the  backward  push 
of  the  wheel,  B,  and  the  downward  weight  of  the  wheel,  D. 
The  resultant  force,  R,  acting  on  a  small  wedge  of  road  surface 
tends  to  split  out  the  material  just  above  it  as  shown  at  A  in 
Fig.  112  (6). 

The  friction  of  the  wheel  against  the  pusned-out  portion 
lifts  it  and  throws  it  into  the  air  as  dust  or  loosened  fragments. 
The  pneumatic  tire  of  the  automobile  does  not  grind  off  new 
dust  to  replace  that  sucked  up  and  blown  away ;  soon  the  road- 
way deprived  of  its  .cementing  property  loosens  and  ravels. 
Again,  if  the  automobile  is  in  the  act  of  starting,  or  stopping, 
or  rounding  a  curve,  or  otherwise  quickly  changing  its  state  of 
motion,  the  component  backward  force  may  become  very  large. 
The  horizontal  pull  on  a  stone  directly  under  the  wheel,  due  to 
friction,  may  be  sufficient  to  cause  it  to  rotate,  as  one  gear  wheel 
acting  upon  another,  which  rotation  will  carry  it  out  of  and 
backward  along  the  pavement.  This  backward  force  may 
actually  shear  off  of  the  surface  thin  flakes  of  road  material,  as 
well  as  throwing  backward  loose  particles  and  dust. 

CRUSHERS  AND  SCREENS 

Where  road  stone  is  plentiful 
near  the  highway  to  be  improved, 
a  portable  crusher  may  advan- 
tageously be  installed.  Such 
crushers  are  usually  of  the  jaw 
type,  Fig.  113,  and  so  arranged 
that  the  crushed  stone  is  elevated 
to  the  revolving  screen  which 
separates  it  into  sizes  and  drops 
it  into  bins  from  which  it  is 
drawn  into  wagons  for  transpor- 
tation to  the  road.  With  the  jaw 
set  for  crushing  two-inch  stone 
the  following  capacities  are  given  for  jaw  crushers: 


FIG.  113. 


CRUSHERS  AND  SCREENS  201 

Size  of  jaw  opening  at  the  top  in  inches 8X16      9X18     10  X  22 

Capacity  in  tons  per  hour 9  to  14     12  to  20     16  to  25 

Horse  power  required 12  15  25 

The  gyratory  crusher,  Fig.  114,  is  quite  extensively  used  in 
permanent  plants.     The  gyratory  crusher  is  said  to  be  more 


FIG.  114. — Portable  Gyratory  Stone  Crusher  and  Elevator. 

durable  than  the  jaw  crusher,  is  very  rapid  and  turns  out  a 
uniform  product.     The  following  specifications  are  given: 

Adaptable  to  portable  plants: 

Receiving  opening  in  inches 7  X  32  8  X  35  10  X  40 

Capacity  in  tons  per  hour 10  to  20  20  to  40  30  to  60 

Horse  power  required 15  to  20  18  to  25  30  to  60 

Adaptable  to  permanent  plants: 

Receiving  opening  in  inches 1.0  X  38  12  X  44     14  X  52 

Capacity  in  tons  per  hour 30  to  70  50  to  90   80  to  120 

Horse  power  required 22  to  30  28  to  45     50  to  75 


CHAPTER  X 
PAVEMENT  FOUNDATIONS 

THE  growing  tendency  to  pave l  rural  roads  with  brick,  Port- 
land cement  concrete,  wood  blocks,  bituminous  macadam, 
bituminous  concrete  and  sheet  asphalt,  makes  it  necessary  to 
touch  briefly  upon  pavements.  Since  the  durability  of  a  pave- 
ment depends  largely  upon  the  stability  of  its  foundation,  this 
chapter  will  be  devoted  to  foundations  entirely. 

Definition. — A  pavement  foundation  for  the  purposes  of  this 
chapter  may  be  denned  as  that  layer  of  the  roadway  differing 

A8phalt  Brick 

Wearlny  Surface 


Binder  Cushion 

Foundation 

Subgrade   or 

Natural  Soil 


FIG.  115. — Typical  Pavement  Sections. 

from  the  original  subgrade  which  is  placed  upon  the  subgrade  to 
reinforce  the  supporting  power  of  it,  Fig.  115.  The  soil  of  the 
subgrade,  as  a  rule,  is  not  sufficiently  rigid  to  support  without 
movement  or  settlement  the  weight  of  the  traffic  and  the  pave- 
ment. A  slight  unevenness  of  the  pavement  surface  soon 
develops  into  a  "  pot  hole  "  or  a  rut.  So  in  best  practice  the 

xThe  special  Committee  on  Road  Materials  of  the  Am.  Soc.  of  Civ. 
Eng.  suggests  this  definition  for  "pavement."  "The  wearing  course  of  the 
roadway  or  footway  when  constructed  with  a  cement  or  bituminous  binder, 
or  composed  of  blocks  or  slabs,  together  with  any  cushion  or  'binder' 
course." 

202 


DEFINITIONS 


203 


roadway  is  made  up  of  two  or  more  layers,  the  lower  one,  resting 
upon  the  natural  subgrade,  being  for  the  purpose  of  strengthen- 
ing or  supporting  the  upper  courses.  The  lower  supporting 
artificial  course  or  courses  comprise  the  foundation,  and, 
specifically,  all  above  this,  the  pavement.  Generally,  however, 
the  word  pavement  includes  the  entire  structure. 

Subgrade. — The  original  earthy  matter — soil,  sand,  gravel, 

rock — upon    which    the    road  7 ~i 

rests  is  the  subgrade  or  base.  .; 

It  evidently  must  bear  the 
weight  of  the  traffic  and  the 
pavement.  The  principal  ob- 
ject of  the  entire  pavement  is 
to  distribute  the  loads  coming 
upon  it  in  such  a  manner  that 
an  undue  amount  shall  not 
fall  on  any  portion  of  the 
subgrade.  If  a  wheel  load  P, 
say,  Fig.  116,  rests  upon  an 
area  A,  it  will  be  distributed 
through  the  pavement  some- 
what in  the  form  of  a  pyramid 


FIG.  116. — Diagram  to  Show  Dis- 
tribution of  Pressure. 


and  if  the  pavement  be  thick  enough,  while  the  intensity  of 
pressure  is  not  the  same  over  the  entire  base  B,1  nowhere  in  the 
base  will  it  exceed  the  safe  bearing  pressure  of  the  subgrade 
material. 

Safe  Bearing  Loads. — Builders  give  the  bearing  loads  per 
square  foot  that  may  be  safely  used  as  follows: 

Tons. 

Solid  rock 12  to  15 

Brick .  .* 8  to  12 

Coarse  sand  or  gravel  in  undisturbed  and  well- 
bonded  strata 6  to    9 

1  Experiments  carried  on  at  the  University  of  Illinois-  found  the  pressure 
through  sand  as  shown  in  Fig.  117  taken  from  an  article  by  M.  L.  Enger, 
in  Engineering  Record,  January  22,  1916.  Showing  the  greater  the  depth 
the  more  uniform  the  pressure  on  any  horizontal  plane  but  that  a  great 
depth  must  be  attained  for  even  near  uniformity. 


204 


PAVEMENT  FOUNDATIONS 


Well-drained  clay 

Moderately  dry  clay 

Loam,  dry 

Sand,  compacted  and  well  held  in  place 


Tons. 
4  to    6 
2  to    8 
2  to    4 
2  to    4 


Illinois  Experiments 
Sand  6" Deep 
Loaded  Area  iti'Diam 
Sighing  Plug  4  'Diam. 


'16          12          8          4  04 

Distance  from  Center  of  Loaded  Area  in  Inches 


Distance  from  Center  of  Loaded  Area  in  Inches 


k  .......  -13.5'D/an  --------  H 


FIG.  117.  —  Distribution  of  Pressure  through  Sand. 


When  clays,  sand  or  soils  become  wet  the  supporting  power 
is  very  greatly  decreased. 


STRENGTHENING  THE   SUBGRADE 


205 


Strengthening  the  Subgrade. — Rolling  the  subgrade  with  a 
moderately  heavy  roller  will  generally  improve  it  and  will  show 
soft  places  such  as  trenches  that  may  have  crossed  the  road, 
animal  burrows,  or  "  springy  "  spots.  Where  sufficient  rigidity 
cannot  be  obtained  by  rolling,  the  soil  may  have  to  be  removed 
and  replaced  by  broken  stone,  gravel,  sand,  clay,  cinders,  shells, 
brickbats,  burnt  gumbo,  clinkers,  slag,  sod,  hay,  brush,  logs, 
plank,  or  whatever  else  may  be  most  available.  In  Massa- 
chusetts a  soft  subsoil  under  a  macadam  road  was  improved  by 
spreading  over  it  a  single  sheet  of  cheesecloth.  This  pre- 
vented the  individual  stones  from  sinking  into  the  mud  and 
made  it  possible  to  consolidate  the  macadam.  Grass,  hay,  and 
brush  have  frequently  been  used  for  a  similar  purpose.  Such 
materials,  when  placed  in  very  wet  places,  even  if  they  do  decay 
after  the  road  is  built,  seldom  do  any  harm.  Plank  has  been 
used  in  swampy  land  and  more  recently  at  Gary,  Ind.,  and 
in  California,  over  very  sandy  places. 

FOUNDATIONS  PROPER 

Stone  Foundations. — Telford,  Fig.  118,  is  a  pavement  of 
roughly  broken  stones  placed  upon  a  subgrade,  usually  parallel 


Telford  Missouri 

FIG.  118. — Stone  Foundations. 


with  the  finished  surface  of  the  road.  The  stones  are  set  up  on 
edge  across  the  road  and  wedged  together  by  spalls.  Project- 
ing portions  above  the  surface  are  knocked  off  and  the  whole 
rolled  with  a  heavy  roller.  This  foundation  for  a  broken-stone 
road  is  desirable  where  the  subgrade  is  quite  wet  and  better 
drainage  than  the  ordinary  macadam  furnishes  is  necessary. 
Missouri. — Large  stones  about  as  heavy  as  one  man  can 


206  PAVEMENT   FOUNDATIONS 

easily  handle  are  put  in  the  bottom,  hit  or  miss,  as  a  foundation 
and  rolled  until  comparatively  of  a  uniform  grade,  Fig.  118. 

Macadam. — Broken  stone  put  in  as  ordinary  macadam  is 
not  an  uncommon  foundation  for  brick  and  bituminous  paved 
roadways.  In  fact,  old  macadam  roadways  swept  clean  and 
leveled  up  with  new  stone  are  frequently  resurfaced  with  paving 
materials. 

V-Drain. — The  subgrade  is  excavated  lower  in  the  middle  so 
as  to  form  a  V-shaped  figure  and  filled  with  boulders  or  broken 
stone,  Fig.  106.  This  furnishes  an  opportunity  for  good 
drainage  under  the  wearing  surface.  Larger  stone  should  be 
placed  in  the  bottom  and  smaller  at  the  top.  In  order  to  allow 
the  water  egress  from  the  center  of  the  roadway,  about  every 
25  to  50  feet,  trenches  are  cut  to  the  side  ditch  and  filled  with 
the  same  kind  of  stones. 

Hydraulic  Cement  Concrete  Foundations. — This  is  by  far 
the  most  important  and  best  type  of  road  foundations.  Either 
"  natural  "  or  "  Portland  "  cement  may  be  used,  though  the 
latter  is  preferable. 

Definition  and  Method  of  Proportioning.1 — Concrete  is  an 
intimate  mixture  of  rock,  broken  stone  or  gravel,  and  sand 
bound  together  by  hydraulic  cement.  Theoretically  the  voids 
in  the  stone  should  be  filled  with  sand  and  the  voids  in  the  sand 
filled  with  cement.  The  grading  of  the  stone  and  sand  should, 
therefore,  be  such  as  to  secure  the  least  possible  amount  of 
resultant  voids.  Experience  has  shown  that  stone  grading 
approximately  uniformly  from  fine  to  coarse,  or  more  exactly, 
according  to  an  elliptical  and  straight-line  curve,  as  shown  in 
Chapter  VII,  will  give  the  densest  and  strongest  mixture.  A 
simple  method  of  proportioning  is  to  determine  the  voids  in  the 
stone  and  sand  and  proceed  as  follows : 

Suppose  voids  in  the  stone =40  per  cent 

Suppose  voids  in  the  sand =35  per  cent 

It  is  customary  to  increase  these  values  so  that  the  sand  will 

overfill  the  voids  in  the  stone  10  per  cent  and  the  cement,  the 

1  See  also  Chapter  XII. 


PROPORTIONING  AND   MEASURING  207 

voids  in  the  sand  10  per  cent,  to  allow  for  the  "  spreading  "  of 
the  stone  by  the  mortar  and  the  spreading  of  sand  particles  by 
the  cement.  For  a  unit  volume  of  concrete  then  take 

Stone =1.00 

Sand,  40%  of  stone  and  10%  of  40% =    .44 

Cement,  35%  of  sand  and  10%  of  35% .  .    =    .  17 

The  ratio  then  is 

Stone  :  sand  :  cement  =  1  :  .44  :     .17 
=  6:    2.6:  1 

That  is,  a  1  :  2.6  :  6  mixture  is  required.  Generally  the  pro- 
portions are  made  easy  aliquot  parts  as  1  :  2.5  :  5,  1:2:4, 
1:3:6,  etc.,  using  a  sack  of  cement  in  mixing,  as  the  unit  and 
measuring  the  other  ingredients  in  terms  of  that  unit. 

Measuring  Aggregates. — The  measurement  is  frequently 
accomplished  by  noting  how 
full  three  or  four  sacks  of 
cement  will  fill  a  wheelbar- 
row and  then  filling  the  sand 
and  stone  accordingly.  A 
more  accurate  plan,  however, 
is  to  have  at  hand  a  measur- 
ing box  by  which  the  wheel- 

,.      ,  „          FIG.  119.— Measuring  Box,  4  cu.  ft. 

barrow  loads  may  be  fre- 
quently and  easily  tested.  Such  a  box  may  be  made  as 
shown  in  the  sketch,  Fig.  119.  Being  bottomless,  by  lifting  on 
the  handles  the  material  falls  on  the  platform  and  can  be  mixed 
directly  with  the  aggregate  or  shoveled  into  the  mixer  with  very 
little  waste  of  time. 

Hand  Mixing. — Two  methods  of  mixing  are  in  use — by 
hand  and  by  machine.  For  the  former,  a  watertight  platform  is 
desirable  on  which  first  is  spread  the  sand,  and  then  the  required 
amount  of  cement.  The  sand  and  cement  are  then  system- 
atically mixed  together.  It  will  be  found  advantageous  to 
have  two  laborers  work  opposite  each  other,  right  and  left- 
handed.  They  should  cut  into  the  pile  which  has  been  ricked 


208  PAVEMENT  FOUNDATIONS 

up  into  a  long,  narrow  windrow,  toward  each  other,  being  sure 
the  shovels  go  each  time  along  the  bottom,  until  they  meet  at 
the  center,  then  lift  the  material  and  turn  it  away  from  the  pile. 
Cut  in  again  until  the  entire  pile  has  been  worked  over  and 
moved  in  the  operation  about  2  feet  backward.  A  reverse 
direction  of  operation  brings  it  back  to  its  original  position. 
The  shovelers  do  more  than  just  turn  the  material  over.  Each 
shovelful  should  leave  the  shovel  with  a  spreading  action  as 
well  as  a  turning.  By  cutting  vertically  into  the  pile  the  suf- 
ficiency of  mixing  can  be  determined.  No  streaks  should 
show ;  all  should  be  of  a  uniform  color.  The  fine  aggregate  now 
mixed  is  spread  out  over  the  board,  the  coarse  material  is  added 
and  turned  in  and  mixed  in  the  same  manner.  Two  turnings 
are  usually  enough.  The  water  is  now  added ;  best  in  the  form 
of  a  spray  and  the  mixing  continued  until  the  entire  mixture 
has  become  wet  and  plastic.  Some  add  the  water  before  mixing 
in  the  stone.  , 

Machine  Mixing. — When  mixed  with  a  machine,  the  sand, 
cement  and  stone  are  dumped  into  the  mixer  followed  almost 
immediately  by  the  water.  The  mixer,  running  at  the  rate  of 
about  thirteen  to  fifteen  revolutions  per  minute,  is  continually 
mixing  the  material;  it  being  carried  up,  turned  over  and 
dropped  several  times  during  each  revolution.  The  turning 
should  continue  long  enough  to  secure  thorough  mixing — each 
particle  of  aggregate  being  coated  with  cement.  A  wet  mix- 
ture is  now  considered  more  likely  to  be  homogeneous  than, 
although  perhaps  not  quite  so  strong,  as  a  drier  mixture  well 
tamped.  By  wet  mixture  is  not  meant  one  that  is  "  soupy," 
but  just  wet  enough  so  that  when  gently  tamped  and  smoothed 
with  the  back  of  the  shovel,  it  will  just  show  water  on  top; 
that  is  a  "  mushy  "  mixture. 

Placing. — After  mixing,  the  concrete  should  be  placed  as 
quickly  as  possible  and  smoothed  by  lightly  tamping.  Any 
perceptible  drying  of  the  concrete  before  or  after  placing  and 
before  setting,  at  which  time  there  is  a  more  or  less  rapid  taking 
up  of  moisture,  is  detrimental  to  the  concrete. 

Protection  during  Hardening. — After  the  concrete  has  set, 


THE  AGGREGATE  209 

if  the  weather  is  warm  and  dry,  it  should  be  protected  from  the 
glaring  of  the  sun  or  be  frequently  sprinkled.  A  week  or  ten 
days  is  usually  allowed  for  hardening  before  the  next  course  is 
laid.  Flooding  or  ponding  with  water  is  also  practiced. 

The  Aggregate. — The  sand  and  stone  or  gravel  together  are 
called  the  aggregate  and  the  cement  the  matrix.  The  aggre- 
gate is  subdivided  into  coarse  and  fine. 

Coarse  Aggregate. — Broken  stone  and  gravel  are  both  used. 
The  stone  being  angular  furnishes  a  greater  mechanical  bond, 
while  the  gravel  being  more  or  less  rounded  packs  closer  and 
makes  a  denser  concrete.  Either  should  be  clean,  free  from  dust 
which  will  prevent  the  adhesion  of  cement. 

Organic  matter  is  detrimental,  therefore  loam  should  be 
excluded;  a  very  small  percentage  of  clay  is  not  detrimental. 
The  size  of  the  largest  stone  will  depend  on  the  type  of  the  work; 
for  road  foundations  1^  inches  down  to  \  inch  is  considered 
about  right — a  graded  mixture  being  better  than  uniformity  in 
size. 

Fine  Aggregate. — Sand  ranging  in  size  from  £-inch  down 
is  most  used.  Stone  screenings  of  the  same  size,  if  free  from 
dust,  are  considered  just  as  good.  Sand  containing  much  mica, 
shale,  clay,  loam  or  silt,  may  require  careful  washing  before 
using.  The  best  sand  is  almost  pure  quartz.  A  small  amount 
of  feldspar  is  not  detrimental.  Since  the  surface  area  of  a 
given  weight  of  sand  rapidly  increases  as  the  size  of  the  grains 
become  smaller,  the  amount  of  sand  a  unit  quantity  of  cement 
will  coat  varies  with  the  fineness.  It  is  estimated  that  1  gram 
of  sand  just  passing  a  10-mesh  sieve,  1.5  millimeters  in  diameter, 
has  a  surface  area  of  15  square  centimeters;  1  gram  just  passing 
a  200-mesh  sieve,  diameter  .08  millimeter,  has  a  surface  area  of 
283  square  centimeters.1  It  will  be  seen,  therefore,  that  1  pound 
of  cement  will  only  paint,  with  the  same  thickness  of  coating, 
15/283  (approximately,  1/19)  as  much  200-mesh  sand  as  it 
will  10-mesh  sand.  Consequently,  the  finer  the  material  the 
more  cement  must  be  used.  On  the  other  hand,  with  irregu- 

1  "  The  Modern  Asphalt  Pavement,"  by  Clifford  Richardson,  1912, 
page  358;  Wiley  &  Sons. 


210  PAVEMENT  FOUNDATIONS 

larly  broken  stone  thrown  together  at  random,  a  uniformly 
screened  size  would  show  more  voids  than  a  graded  mixture.1 
Therefore,  it  is  more  economical  to  use  a  graded  mixture  from 
the  finest  sand  to  the  coarsest  rock  allowable.  With  average 
graded  materials  a  1:3:6  mixture  makes  a  good  pavement 
foundation. 

Concrete  Manufactured  in  Place. — A  layer  similar  to  the 
bottom  course  of  a  macadam  road  is  placed  and  rolled.  A  1  :  3 
mixture  of  cement  and  sand  is  spread  uniformly  over  the  sur- 
face and  swept  in.  The  surface  is  then  flushed  with  water  and 
more  cement  and  sand  distributed  until  the  interstices  are  com- 
pletely closed.  The  surface  is  continually  rolled  during  the 
process  of  filling. 

Another  plan  is  to  mix  the  sand  and  cement  to  a  grout  of 
creamy  consistency  in  boxes  and  then  fill  the  interstices,  rolling 
and  grouting  until  the  voids  are  closed.  This  is  a  patented 
method;  the  patentees  use  a  1  :  4  grout. 

Concrete  slabs  may  be  molded  in  a  factory,  transported  to 
and  laid  upon  the  prepared  subgrade.  A  thin  sand  cushion  on 
the  subgrade  can  be  readily  struck  off  to  a  uniform  surface  and 
by  furnishing  a  good  bearing  will  prevent  cracking. 

Bituminous  concrete  foundations  have  been  used,  the 
manufacturers  claim,  very  successfully,  but  are  not  as  cheap 
or  rigid  as  hydraulic  concrete. 

Brick. — Old  brick  pavements  which  have  worn  uneven  have 
been  used  frequently  and  successfully  for  foundations  for  sheet 
asphalt  and  asphaltic  macadam  pavements.  Stone  blocks  may 
be  used  in  the  same  manner. 

1  The  percentage  of  voids  with  spheres  of  uniform  size  is  the  same  no 
matter  what  the  diameter  of  the  spheres. 


CHAPTER  XI 
BRICK,  STONE,  WOOD,  AND   OTHER  BLOCK  ROADS 

As  here  used  "  block  roads  "  refers  to  those  the  wearing 
surface  of  which  is  composed  of  blocks  that  have  been  made  or 
prepared  prior  to  being  placed  in  the  road.  Only  the  following, 
suitable  for  country  roads,  will  be  mentioned:  Brick,  stone 
block,  "concrete  block,  wood  block,  bituminous  block,  and 
bituminized  brick. 

BRICK  ROADS 

Vitrified  Paving  Brick. — Shales  and  impure  fire  clays  have 
proven  themselves  best  adapted  for  the  manufacture  of  paving 
brick.  In  order  to  insure  the  requisite  shape,  hardness  and 
toughness,  the  clay  in  the  process  of  manufacture  mus.t  be  both 
plastic  and  fusible  and  at  the  same  time  capable  of  retaining 
its  shape  under  intense  heat.  The  shales,  which  are  clays  that 
have  undergone  physical  and  possibly  chemical  changes,  becom- 
ing hardened  and  laminated,  possess  these  properties  in  a 
much  greater  degree  than  do  the  later  formed  surface  clays. 
Approximately  the  following  composition  is  required  for  a  good 
paving  brick: 1 

Per  Cent 

Silica 56 

Alumina 22 . 5 

Flux ' 13 

Volatile  matter 8.5 

The  flux  may  be  various  oxides  of  iron,  lime,  magnesia,  or  other 
minerals.  The  volatile  matter  is  water  of  crystallization  and 
organic. 

Shales  from  different  deposits  are  seldom  alike;  they  require 

1  Blanchard  and  Brown's  "Highway  Engineering,"  Wiley  &  Sons,  N.Y. 

211 


212     BRICK,  STONE,  WOOD,  AND  OTHER  BLOCK  ROADS 


different  treatment  in  the  process  of  manfacture  to  obtain  best 
results.  Scientific  and  experimental  study  of  each  individual 
deposit  is  necessary,  and  ingredients  may  have  to  be  brought 
from  different  localities  and  mixed.  The  shale  deposits  used, 
however,  are  generally  open  pits  and  the  material  is  obtained 
therefrom  by  means  of  steam  shovels.  The  shale,  if  not  of  an 
easy  variety,  is  crushed  in  grinding  mills  or  by  large  rolls  running 
in  a  pan  having  gratings  for  its  bottom.  The  screened  material 
is  mixed  with  water  in  a  pug  mill  to  the  proper  consistency. 
The  pug  mill  is  a  trough  in  which  revolves  a  shaft,  or  shafts, 
with  attached  ringers  or  blades  that  passing  through  the 
mud  work  it  up  to  the  point  of  greatest  plasticity.  The  fingers 
of  the  pug  mill  are  arranged  in  a  spiral  form  about  the  shaft  or 
flattened  and  turned  a  little  so  as  slowly  to  move  the  mud 
toward  the  molding  machine  in  which  is  an  auger  that  in 

turn  forces  it  through  the 
die.  The  mud  comes  from 
the  die  in  the  form  of  a  prism 
and  as  it  passes  along  is  cut 
by  wires  on  a  suitable  frame- 
work into  bricks.  The  ma- 
chine operating  the  cutting 
wires  either  causes  a  plane 
surface  cut  along  the  side  of 
the  brick  or  a  warped  cut 
which  forms  a  lug.  The  plane- 
cut  brick  are,  by  one  process 
placed  in  a  receptacle,  where 
they  are  re-pressed;  at  the 
same  time  the  corners  are 
rounded  off  and  the  lugs, 
grooves  and  brand  of  brick 
are  stamped  on  the  side,  Fig. 
120.  "  Vertical  fiber  "  1'rick 

have  grooves  and  lugs  formed  by  the  die,1  in  which  case  the 

i 

1  Brick  are  now  being  made  without  lugs  of  any  kind,  the  lug  being 
considered  unnecessary  when  a  thin  filler)  such  as  grout  or  pitch'is  used. 


FIG.  120. — Paving  Brick. 


BRICK  MANUFACTURE  213 

brick  are  laid  in  the  street  with  a  cut  surface  up.  The  wabbly 
or  warped  surface  cut  is  characteristic  of  what  are  known 
commercially  as  "  wire-cut-lug ."  brick,  Fig.  120.  There  has 
been  much  contention  among  manufacturers  as  to  the  relative 
merits  of  "  re-pressed,"  "  vertical  fiber,"  and  "  wire-cut-lug  " 
brick.  Good  pavements  have  been  made  of  .all  kinds.  If  they 
will  stand  the  rattler  test  they  will  probably  prove  to  be  satis- 
factory. 

The  molded  brick  are  placed  on  cars  in  such  a  manner  that 
there  may  be  a  free  circulation  of  air  about  them  and  taken  to 
the  drying  chambers.  These  are  usually  heated  by  the  escaping 
hot  gases  from  the  kilns  or  by  air  forced  through  the  burned  kiln 
to  cool  it.  The  heated  air  comes  into  the  drying  chamber  at 
the  "  dry  "  end  and  as  it  passes  along  it  takes  up  moisture  and 
loses  heat.  When  it  reaches  the  "  green  "  end  it  is  moist  and 
comparatively  cool.  The  cars  of  brick  are  from  time  to  time 
moved  along  through  the  drying  chambers,  a  "  dry "  car 
being  pushed  out  and  a  "  green  "  car  in.  It  takes  from  one  to 
three  days  to  dry  the  brick,  as  this  must  be  done  slowly  enough 
to  prevent  checking.  The  brick  are  then  burned,  usually  in 
down-draft  kilns,  from  seven  to  ten  days.  The  temperature 
necessary  to  burn  brick  is  a  cherry  red,  that  is,  1500  to  2000°  F. 
for  shales,  and  2000  to  2800°  F.  for  impure  fire  clays  and  requires 
from  seven  to  ten  days.  The  temperature  will  depend  on 
the  clay  used  and  the  character  and  quantity  of  the  fluxing 
ingredients.  While  vitrification  or  melting  down  should  be 
incipient,  it  must  not  proceed  far  enough  to  destroy  the  shape 
of  the  brick.  When  the  brick  are  sufficiently  burned  the  kiln 
is  tightly  closed  and  allowed  to  stand  for  several  days.  The 
brick  are  thus  annealed  and  acquire  toughness.  After  annealing 
the  final  cooling  may  be  more  rapid,  and  the  air  drawn  through 
the  kiln  to  cool  it  may  be  used  in  the  drying  chambers.  In  the 
best  kilns  some  of  the  brick  will  not  be  first  class.  Upon  open- 
ing the  kiln  the  brick  must  be  sorted  into  No.  1  pavers,  No.  2 
pavers,  and  builders.  With  impure  fire  clay  as  high  as  80  to  90 
per  cent  of  the  kiln  are  No.  1  pavers;  with  shale  the  percentage 
is  60  to  80. 


214     BRICK,  STONE,  WOOD,  AND  OTHER  BLOCK  ROADS 

TESTING  PAVING  BRICK 

The  quality  and  acceptability  of  paving  brick  are  usually 
made  to  depend  on  the  specifications  of  the  American  Society 
for  Testing  Materials  and  those  of  the  National  Paving  Brick 
Manufacturers  Association.  These  are,  in  brief,  the  Rattler 
Test  and  Visual  Inspection.  The  rattler  test  is  "  for  the  pur- 
pose of  determining  whether  the  material  as  a  whole  possesses 
to  a  sufficient  degree  strength,  toughness  and  hardness."  Vis- 
ual inspection  is  "  for  the  purpose  of  determining  whether  the 
physical  properties  of  the  material  as  to  dimensions,  accuracy 
and  uniformity  of  shape  and  color,  are  in  general  satisfactory, 
and  for  the  purpose  of  culling  out  from  the  shipment  individually 
imperfect  or  unsatisfactory  brick." 

The  Rattler  Test. — The  samples  are  taken  either  at  the 

brick  factory  or  at  the 
locality  where  used  depend- 
ing upon  the  size  of  the 
shipment.  The  samples  se- 
lected should  be  as  near  as 
possible  an  average  of  the 
shipment.  One  sample  of 
ten  bricks  for  each  10,000 
bricks  contained  in  the 
lot  under  consideration  is 
taken,  and  care  should  be 
FIG.  121.— Standard  Brick  Rattler.  used  that  samples  are  not 

damaged  in  transportation 

or  otherwise  before  testing.  The  rattler,1  Fig.  121,  is  a 
barrel-like  chamber,  28  inches  in  diameter  by  20  inches 
length  inside  measure,  in  which  the  sample  is  tumbled  with 
cast-iron  shot.  The  percentage,  by  weight,  of  the  brick 
worn  away  in  1800  turns  accomplished  in  one  hour,  is  a 
measure  of  the  quality  of  the  brick.  The  charge  of  the  rattler 
consists  of  the  sample  of  brick,  ten  in  number  for  ordinary 

1  For  complete  specifications  see  standards  of  the  American  Society 
%  for  Testing  Materials,  1918,  p.  549. 


TESTING  AND  INSPECTION 


215 


sizes  (length  8  to  9  inches,  breadth  3  to  3f  inches,  thickness 
3f  to  4|  inches),  and  of  a  quality  passing  the  visual  inspection 
test,  together  with  the  abrasive  shot.  The  shot  consists  of 
cast-iron  spheres  of  two  sizes.  The  larger,  when  new  are  3.75 
inches  in  diameter  weighing  approximately  7.5  pounds  (3.40 
kilograms)  each,  and  ten  are  used.  The  weight  of  no  sphere 
shall  be  less  than  7  pounds.  When  new,  the  smaller  spheres 
are  1.875  inches  in  diameter  and  weigh  approximately  0.95 
pound  (0.43  kilogram)  each.  No  sphere  shall  be  retained  in 
use  after  it  has  worn  down  so  that  its  diameter  is  less  than  1.75 


Sand  Cushion 


Cross-Section  of  Brick  Rural  Road 


Sand-Cushion 


Green-Cement 
SanL-Ci-ment 


FIG.  122.— Brick  Pavement. 

inches  or  weighs  less  than  0.75  pound  (0.34  kilogram).  The 
collective  weight  of  the  large  and  small  spheres  shall  be  as 
near  300  pounds  as  possible. 

The  following  scale  of  average  losses  is  given;  the  per- 
centage for  rejection  on  any  particular  job  should  be  specified 
by  the  engineer  in  charge  or  the  buyer: 

i     For  bricks  suitable  for  heavy  traffic 20  to  24 

For  bricks  suitable  for  medium  traffic 22  to  26 

For  bricks  suitable  for  light  traffic 24  to  28 

A  great  many  shale  bricks  will  give  losses  as  low  as  15  per  cent. 
Visual  Inspection. — Bricks  that  are  broken  in  two  or  chipped 


216     BRICK,  STONE,  WOOD,  AND  OTHER  BLOCK  ROADS 

so  that  neither  surface  remains  intact  or  so  that  the  lower  or 
bearing  surface  is  reduced  in  area  by  more  than  one-fifth;  or 
are  cracked  in  such  a  degree  as  to  produce  such  defects,  either 
from  shocks  received  in  shipment  or  in  drying,  burning  and 
cooling;  or  bricks  which  are  off  size,  or  so  misshapen,  bent, 


Sect/o/j  ;fl  md  lateral  Drain» 


r* 

Longitudinal  Drains 


^s^p^sfcr 

Section  14         Blind  Lateral  DraiKt 


Detail  of  Cur*  Detail  of  Curb 

FIG.  123. — Illinois  Standard  Cross-sections  for  Single-track  and   Double- 
track  Brick  Roads. 

Section  10 — Ten-foot  roadway  with  4-ft.  macadam  shoulders.  To  be  used  in  a  level 
country.  Section  11 — Ten-foot  brick  roadway  with  4-ft.  macadam  shoulders  and  broad 
side  ditches  available  for  traffic  where  width  between  fences  permits.  Especially  adapt- 
able for  low-lying  level  country.  Section  12 — Ten-foot  brick  roadway  with  4-ft.  mac- 
adam shoulders.  To  be  used  on  deep  fills.  For  shallow  fills  use  Section  1.  Section 
13 — Fifteen-foot  brick  roadway  for  single-track  road  in  deep  cuts  and  on  grades  that 
require  grouted  gutters.  Section  14 — Eighteen-foot  brick  roadway.  To  be  used  in  a 
level  country.  Section  15 — Eighteen-foot  brick  roadway  with  broad  side  ditches, 
available  for  traffic  where  width  between  fences  permits.  Especially  adaptable  for 
low-lying  level  country.  Section  16 — Eighteen-foot  brick  roadway.  To  be  used  on 
deep  fills.  For  shallow  fills  use  Section  1.  Section  17 — Eighteen-foot  brick  roadway  for 
double-track  road  in  deep  cuts  and  on  grades  that  require  grouted  gutters. 

twisted  or  kiln  marked,  that  they  will  not  form  a  proper  surface ; 
and  all  bricks  which  are  obviously  too  soft  or  too  poorly  vitrified 
to  endure  street  wear  should  be  culled  out  and  rejected.  Color, 
in  itself,  is  no  criterion  of  a  brick's  quality.  Bricks  from  differ- 
ent plants  vary  greatly.  But  color  may  be  used  to  assist  in 
comparing  bricks  from  the  same  plant. 


CURBS.     FOUNDATIONS  217 

- 

DESIGN  AND  CONSTRUCTION  OF  BRICK  ROADS 

Figs.  122  and  123  show  recommended  cross-sections  of 
modern  brick  construction. 

Subgrade  and  Drainage. — The  building  of  the  subgrade 
and  the  drainage  should  be  as  carefully  looked  after  as  for  any 
other  kind  of  roadway. 

Curbing. — In  order  to  prevent  the  margins  from  loosening  a 
curb  is  generally  supplied. 
This  may  be  of  natural  or 
artificial  stone,  oak  plank,  or 
merely  bricks  placed  on  end. 
Where  the  shoulders  outside  v  (a)  ^  (b) 
the  brick  roadway  are  mac-  FlQ  124>_Curbs  for  Brick 
adam  no  marginal  curb  need 
be  used.  Also  in  monolithic  (green-cement  or  sand-cement) 
construction  curbs  are  not  required. 

Natural  stone  curb  may  be  about  12  inches  wide  and  4 
inches  thick.  These  stones  should  be  hauled  and  set  in  place 
before  the  grading  is  completed.  They  will  then  serve  as  a 
guide  to  finish  the  subgrade  and  place  the  concrete  foundation. 
Artificial  stone,  cast  in  the  factory  may  be  used  in  the  same  way. 

Forms  of  plank  can  easily  be  erected  and  concrete  curbs 
cast  in  place  either  before,  at  the  same  time  or  after  placing 
the  foundation.  Or  wood  blocks  may  be  used  to  fill  out  the 
ends  of  the  brick  courses,  later  removed  and  a  curb  cast  in  place 
which  will  interlock  with  the  brick.  •  This  is  done  after  the  brick 
is  rolled  and  just  before  the  grouting  is  poured.  Plank  or 
brick  set  on  end  will  offer  no  difficulties.  The  brick  will  hold 
better  if  cement  mortar  is  "  spaded  in  "  back  of  them,  but  the 
cost  will  be  greater. 

Foundation. — Brick  pavements  have  been  laid  on  earth 
foundations,  on  a  course  of  cheaper  brick  laid  flatwise,  on 
macadam  and  on  concrete. 

Concrete  foundations  are  to  be  recommended.  They  have 
the  power  to  bridge  or  arch  over  a  short  soft  spot  and  thereby 
prevent  depressions  and  unevenness  of  surface  due  to  unequal 


218     BRICK,  STONE,  WOOD,  AND  OTHER  BLOCK  ROADS 

settlement.  Maintaining  an  even  smooth  surface  is  an  essen- 
tial factor  in  the  durability  of  a  pavement. 

Where  a  cheaper  grade  of  brick  is  used  for  a  foundation, 
they  are  laid  flatwise  on  a  2-inch  cushion  of  sand  and  rolled 
to  surface.  A  grout  is  sometimes  made  of  1  part  Portland 
cement  and  2  parts  clean  sand  with  which  the  spaces  between 
the  bricks  are  thoroughly  filled. 

Sand  Cushion. — A  layer  of  sand  1J  to  2  inches  thick  is 
placed  upon  the  foundation  and  spread  to  an  even  surface  by 
aid  of  a  template.  It  should  be  clean  and  free  from  foreign  or 
loamy  matter.  It  need  not  be  sharp.  This  cushion  furnishes  a 
smooth  even  surface  to  rest  the  brick  upon,  insures  good  bearing 
over  the  entire  lower  surface  of  the  brick,  and  lessens  noise 
which  in  places  may  be  annoying,  Fig.  122. 

Laying  the  Brick: — The  brick  should  be  laid  at  right  angles 
to  the  curb  or  length  of  the  roadway.  At  turns  or  road  inter- 
sections they  may  be  placed  at  an  angle  of  45°.  The  brick 
should  be  laid  with  best  edge  uppermost  as  near  in  contact  as 
possible.  Soft  brick  or  those  badly  checked  and  spalled  should 
be  removed  and  discarded. 

Rolling. — After  the  brick  in  the  pavement  are  inspected 
and  the  spalls  swept  off,  they  should  be  rolled  with  a  roller  of 
about  4  tons  weight.  Brick  that  cannot  be  reached  by  the  roller 
should  be  thoroughly  tamped  with  a  wooden  tamper.  Rolling 
should  begin  at  the  outside  shoulders  and  proceed  gradually 
toward  the  center.  If  the  roadway  is  wide  enough  to  justify, 
it  should  also  be  rolled  diagonally  at  an  angle  of  45°  to  the  curb. 

Expansion  Joints. — If  the  roadway  is  more  than  25  feet 
wide  expansion  joints  are  required.  These  are  made  by  placing 
1-inch  boards  longitudinally  along  the  curb  and  about  every  50 
feet  transversely  across  the  roadway.  After  the  rolling  is 
completed,  the  boards  are  withdrawn  and  the  spaces  filled  with 
asphalt  or  pitch.  Patented  fiber  expansion-joint  material  can 
be  purchased.  This  is  put  in  like  the  boards  and  allowed  to 
remain.  The  National  Paving  Brick  Manufacturers  Associa- 
tion recommends  the  omission  of  transverse  expansion  joints. 

The  Filler. — The  spaces  between  the  bricks  should  be  filled 


JOINT  GROUTING 


219 


with  Portland  cement  grout  or  a  bituminous  filler.  Formerly 
dry  sand  was  used,  but  of  late  years  this  has  been  practically 
discontinued.  Portland  cement  grout  filler  should  be  composed 
of  one  part  cement  to  one  part  sand  that  is  free  from  loam, 
clay  or  other  foreign  matter.  Sharpness  is  not  a  requisite. 
Sand  and  cement  in  equal  volumes  are  placed  in  a  box,  Fig.  125, 
and  mixed  until  of  a  uniform  color.  Enough  water  is  then 
added  to  form  a  grout  of  the  consistency  of  thin  cream.  The 
sides  and  edges  of  the  brick  should  be  wet  before  the  filler  is 
applied.  The  creamy  grout  may  be  shoveled  on  the  pave- 
ment from  the  box  with  a  scoop-shovel.  Care  being  taken 


FIG.  125. — Recommended  Grouting  Box. 

that  the  grout  be  constantly  agitated  during  the  entire  process. 
The  grout  must  be  immediately  broomed  into  the  joints.  After 
covering  thus  a  distance  of  15  or  20  yards  the  force  should  be 
turned  back  and  cover  again  with  a  richer  grout  composed  of  2 
parts  Portland  cement  to  1  part  sand.  After  the  joints  have 
been  entirely  filled  and  time  has  elapsed  for  the  cement  to  set  a 
J-inch  coating  of  sand  should  be  spread.  An  occasional  sprin- 
kling with  water  for  two  or  three  days  is  necessary  to  harden 
the  cement  properly. 

The  Illinois  Highway  Department l  is  very  particular  about 
the  grouting  and  specifies  a  1  cement  to  1  sand  grout  mixed 

1  See  statement  by  H.  E.  Bilger,  Road  Engineer,  Illinois  Highway 
Department,  in  Engineering  and  Contracting,  Dec.  6,  1916. 


220     BRICK,  STONE,  WOOD,  AND  OTHER  BLOCK  ROADS 

dry,  then  with  water  to  the  consistency  of  cream.  This  is  shov- 
eled from  the  box  to  the  pavement,  which  has  been  thoroughly 
wetted,  and  broomed  into  the  openings  between  the  brick. 
After  about  200  feet  is  filled  the  gang  is  turned  back  to  the 
place  of  beginning  and  the  surface  gone  over  again  in  the  same 
manner  except  that  the  consistency  is  a  little  thicker  and  a 
squeegee  replaces  the  rattan  broom  for  pushing  the  grout  into 
the  cracks.  This  is  repeated  as  many  times  as  may  be  neces- 
sary. The  statement  is  made  that  one  barrel  of  cement  will 
make  sufficient  grout  to  cover  the  area  below: 

4-inch  brick  on  ordinary  sand  cushion. 
32  square  yards  if  repressed  brick  is  used. 
24  square  yards  if  wire-cut  lug  brick  is  used. 

4-inch  brick  on  f-inch  mortar  bed. 

30  square  yards  if  repressed  brick  is  used. 

22  square  yards  if  wire-cut  lug  brick  is  used. 

The  American  Society  for  Testing  Materials  specifications  l 
require  the  Portland  cement  to  conform  to  their  standards; 
the  sand  is  to  be  of  clean,  hard,  durable  stone,  preferably 
siliceous  and  free  from  clay  or  other  foreign  objectionable 
matter;  the  sand  is  to  be  well  graded  and  must  meet  the 
following : 

Total  passing    10-mesh  sieve 100  per  cent 

Total  passing    20-mesh  sieve  not  less  than.     80      " 
Total  passing  200-mesh  sieve  not  more  than      5      " 

The  mortar  made  from  1  cement  to  3  of  this  sand  at  the  ages 
of  7  and  28  days  shall  have  at  least  75  per  cent  of  the 
strength  of  similar  mixtures  and  ages  with  standard  Ottawa 
sand. 

Bituminous  Filler. — Coal-tar  pitch  and  asphalt  are  both 
good  fillers.  Care  must  be  taken  that  the  filler  will  retain  a 
suitable  consistency  under  extreme  temperatures.  American 
Society  for  Municipal  Improvements  specifications  require  for 
coal  tar: 

!"  A.  S.  T.  M.  Standards  Adopted  in  1920,"  p.  80. 


BITUMINOUS  JOINT  FILLER  221 

Specific  gravity,  15.5°  C.  (60°  F.),  1-23  to  1.35. 
Melting-point,  cube  method,  46°  to  57°  C.  (115  to  135°  F.) 
Inorganic  matter,  not  more  than,  0.5  per  cent. 
Ductility  at  25°  C.  (77°  F.),  not  less  than  60  centimeters. 

Typical  specifications  for  asphalt  require: 

Specific  gravity,  not  less  than,  0.98. 

Penetration  at  25°  C.  (77°  F.),  60  to  100. 

Distillation  loss  163°  C.  (325°  F.),  not  more  than  3  per  cent. 

Penetration  of  residue,  25°  C.  (77°  F.),  not  less  than  50. 

Melting-point,  ring  and  ball  method,  not  less  than  80. 

Pouring. — The  filler  is  heated  to  a  temperature  between 
149  and  177°  C.  (300  to  350°  F.)  and  poured  into  the  joints. 
A  can  in  the  form  of  an  inverted  cone  with  an  opening  at  the 
smaller,  lower  end,  is  convenient.  The  workman  moves  this 
along  the  joint  to  be  filled  and  regulates  the  flow  by  means  of  an 
iron  rod  passing  down  to  a  stopper  at  the  opening  at  the  small 
end  of  the  can.  Bituminous  fillers  have  the  advantage  that  no 
expansion  joints  are  needed  and  the  pavement  is  less  noisy  than 
the  grout  filled.  The  disadvantages  are  a  tendency  to-"  bleed  " 
in  hot  weather  and  to  crack  in  cold  weather.  The  claim  is 
made,  also,  that  bituminous-filled  bricks  are  inclined  to  chip 
off  at  the  upper  edges  and  become  "  turtle  backed."  With  a 
filler  of  right  consistency  this,  however,  seldom  occurs.  After 
filling,  a  thin  sprinkling  of  sand  will  take  up  the  surplus  bitumi- 
nous cement. 

Paint  Coat. — Some  engineers  require  a  paint  coat  of  hot 
asphalt  or  tar  over  the  entire  pavement.  This  is  thinly  sprinkled 
with  sand  or  stone  screenings.  It  serves  to  give  a  surface  as 
smooth  as  asphalt  and  if  renewed  every  year  or  two  will  pre- 
serve the  pavement  indefinitely.  The  paint  coat  is  put  on  with 
a  "  squeegee,"  that  is,  an  apparatus  which  allows  a  stream  of 
hot  pitch  to  flow  onto  the  pavement  in  front  of  a  wooden  block 
on  which  is  nailed  a  strip  of  rubber  belting  which  spreads  and 
rubs  the  pitch  thinly  on  the  pavement.  Brick  manufacturers, 
as  a  rule,  do  not  recommend  a  paint  coat. 


222     BRICK,  STONE,  WOOD,  AND  OTHER  BLOCK  ROADS 

MONOLITHIC  BRICK  PAVEMENT 

Bedding  Method. — A  coating  or  bed  of  cement  mortar  is 
spread  on  the*  concrete  foundation  and  the  brick  laid  in  this 
mortar  and  as  quickly  as  possible  rolled  or  tamped  to  an  even 
surface.  The  mortar  furnishes  a  bond  between  the  brick  and 
foundation  of  about  the  same  kind  as  between  bricks  in  a  wall. 

Paris  or  Cement-sand  Method. — (So  called  because  used  at 
Paris,  111.)  Cement  and  sand  properly  proportioned  (1 
cement  to  4  sand  is  recommended)  are  thoroughly  mixed  dry  in  a 
a  mixer  or  by  hand.  The  mixture  is  spread  uniformly  over  the 
prepared  concrete  foundation  about  1  inch  thick,  compressed 
with  a  300-pound  roller  and  struck  off  with  a  template  to  the 
true  contour  of  the  pavement.  If  any  depressions  occur  they 
should  be  filled  and  the  "  cement-sand  "  bed  again  rolled  and 
struck  off.  The  bricks  are  immediately  laid,  inspected  and 
rolled.  It  is  quite  necessary  specially  to  prepare  the  cement 
foundation.  A  substantial  template  or  double  template  is 
drawn  over  the  plastic  foundation  bringing  it  to  exact  contour. 
As  soon  as  the  foundation  has  sufficiently  hardened  to  stand  the 
pressure  the  cement-sand  is  distributed  and  brick  laid.  The 
setting  of  the  cement-sand  layer  and  its  proper  binding  to  the 
foundation  and  the  brick  is  said  to  be  best  when  it  takes  up 
sufficient  water  from  the  foundation  to  moisten  it  thoroughly. 
Tests  show  a  remarkable  adhesion  of  the  bricks  and  foundation 
by  this  process.  It  is  claimed  that  the  cement-sand  course 
eventually  becomes  part  of  the  foundation,  so  that  if  a  5-inch 
foundation  is  needed,  it  should  be  designed  4  inches  of  concrete 
and  1  inch  of  cement-sand.  Before  filling  with  cement  grouting 
the  brick  should  be  wet  down  with  a  spray,  this  insures  the 
setting  up  of  the  binder  c'ourse  even  had  it  not  taken  up  enough 
moisture  from  the  foundation. 

Direct  Method. — Another  form  of  monolithic  construction  is 
obtained  by  laying  the  brick  directly  on  the  concrete  founda- 
tion without  the  use  of  the  cement-sand  course.  The  founda- 
tion is  finally  finished  to  exact  contour  by  means  of  a  wooden 
tamping  template.  This  is  moved  along  the  side  forms  with 


GREEN   CEMENT  BRICK  PAVEMENT 


223 


a  simple  tamping  motion  bringing  the  mortar  of  the  concrete 
to  the  surface,  leaving  a  smooth  bed  on  which  to  drop  the 
brick.  For  wide  streets  guiding  strips  set  along  the  street  to 
proper  grade  are  used.  Small  bridges  or  stools  must  be  provided 
for  the  men  to  stand  upon.  These  with  the  strips  are  moved 
along  and  depressions  filled.  The  laying  of  the  brick  closely 
follows.  The  brick  should  be  laid,  rolled  and  inspected  before 
the  concrete  takes  its  initial  set. 

Green  Cement  Method. — A  variation  or  combination  of  the 
above  methods  known  as  the  green  cement  method  is  recom- 
mended by  the  National  Paving  Brick  Manufacturers'  Associa- 


FIG.  126. — Laying  Monolithic  Brick  Pavement. 

tion.  The  concrete  foundation  is  brought  approximately  to 
grade  by  spading  and  settling  and  finished  for  the  brick  with  a 
double  template  consisting  of  a  6-inch  I-beam  in  front  and  a 
6-inch  I-beam  or  channel  in  the  rear,  Fig.  126.  These  are  to  be 
held  rigidly  upright  by  framing  them  together,  parallel  and  2 
feet  apart.  •  The  rear  channel  is  to  be  -f$  inch  higher  than  the 
front.  Rollers  attached  to  the  frame  and  resting  on  the  guide 
rails  facilitate  moving  the  template  along.  As  the  template  is 
pulled  forward  the  front  parallel  member  strikes  off  the  roughly 
deposited  concrete.  A  dry  mixture  of  the  fine  aggregate  and 
cement  in  the  proportion  of  one  part  cement  to  three  parts 


224     BRICK,  STONE,  WOOD,  AND  OTHER  BLOCK  ROADS 

sand  is  placed  between  the  parallel  members  of  the  template; 
this  is  spread  by  the  rear  channel  uniformly  ^  inch  thick  over  the 
struck-off  concrete.  It  immediately  takes  up  moisture  from 
the  concrete  and  becomes  an  integral  part  of  it,  Fig.  127,  The 
brick  are  carried  from  the  piles  and  placed  convenient  to  the 
dropper  in  such  a  manner  that  their  projections  are  all  in  one 
direction  and  the  better  edge  uppermost.  The  dropper  then 


FIG.  127. — Green  Cement  Pavements,  Courtesy  of  Nat.  Pav.  Brick  Mfg; 

Assn. 

lays  them  upon  the  prepared  surface.  Alternate  layers  begin 
with  a  half -brick  in  order  that  joints  may  be  broken;'  the  broken 
end  of  the  half -brick  should  be  inward.  Each  course  should  be 
laid  true  and  even  and  closed  and  straightened  by  tapping 
lightly  with  a  sledge  or  a  4X4  timber  3  feet  in  length  with  an, 
upright  handle. 

Inspecting  and  Rolling. — Immediately  after  laying,,  the  brick 


STONE   BLOCK   PAVEMENTS  225 

should  be  swept  clean,  the  brick  inspected,  those  not  having 
the  better  edge  upward  turned  over,  and  broken  and  poor  brick 
rejected.  The  pavement  should  then  be  rolled  with  a  hand  roller 
approximately  30  inches  long  and  24  inches  in  diameter,  made  in 
sections  and  filled  with  water,  weighing  not  less  than  20  pounds 
per  inch  of  length.  The  rolling  should  be  kept  close  to  the 
laying  and  continued  until  the  surface  is  smooth.  Such  portion 
of  the  surface  as  may  be  inaccessible  to  the  roller  should  be 
brought  to  an  even  surface  by  tamping  upon  a  2-inch  board. 
At  the  end  of  the  day,  no*  matter  which  method  is  used,  the 
laying,  inspection  and  rolling  should  be  completed  to  the  limit 
of  the  foundation.  Grouting  may  be  done  the  following  day. 

On  country  roads  the  edging  or  curb  may  be  omitted,  as  the 
brick  are  so  firmly  bound  to  the  foundation  that  it  is  not  needed. 
A  shoulder  of  earth  or  broken  stone,  however,  should  be  pro- 
vided for  use  in  turning  out  and  to  prevent  chipping  the  edges 
of  the  bricks. 

Maintenance. — The  maintenance  of  a  brick  road  consists 
in  replacing  soft  or  broken  bricks  as  they  appear  through  action 
of  frost,  excessive  loads  or  such  as  may  be  caused  by  the  lug  of  a 
traction  engine.  A  squeegee  coat  of  bituminous  material  placed 
every  one  or  two  years  will  help  maintain  a  smooth  surface  and 
increase  the  durability  of  the  pavement.  The  average  life  of  a 
brick  pavement  has  been  given  as  fifteen  years,  but  if  brick  of  a 
uniform  quality  are  well  laid  upon  a  good  foundation  they  ought 
to  last  on  an  ordinary  country  road  for  at  least  fifty  years. 

STONE  BLOCK  PAVEMENTS 

Stone  block,  while  one  of  the  oldest  and  most  durable  pave- 
ments, is  not  in  general  use  for  country  roads;  it  is  used  in 
cities  and  villages  about  warehouses  and  depots  where  the 
traffic  is  heavy.  The  reader  should  look  for  a  more  extended 
and  detailed  discussion  in  works  dealing  directly  with  city 
pavements. 

Size  of  Blocks. — In  the  very  early  period  of  road  building 
the  stone  blocks  used  for  surfacing,  as  in  the  noted  Roman 
roads,  were  irregular  in  shape  arid  dimensions  and  were  fitted 


226     BRICK,  STONE,  WOOD,  AND  OTHER  BLOCK  ROADS 

together  in  a  sort  of  hit  or  miss  mosaic.  In  our  own  country 
some  communities  are  still  using  cobble-stone  pavements  laid 
before  the  Civil  War  of  small  bowlders  or  rounded  field  stones.1 
Modern  methods  demand  that  the  stones  after^  quarrying  be 
split  into  nearly  uniform  sizes"  of  approximately  8  to  12  inches 
long,  3i  to  4J  inches  wide,  and  4f  to  5|  inches  deep.  The 
number  of  blocks  per  square  yard  of  surface  runs  from  28  to  32. 

Physical  Properties. — Good  paving  block  stone 'should  be 
of  such  a  character  that  it  will  break  easily  into  the  required 
sizes  and  have  a  comparatively  smooth  surface;  it  should  be 
moderately  hard,  tough  and  durable;  and  so  homogeneous  that 
it  will  wear  uniformly.-  Under  wear  it  should  retain  a  grit 
and  not  become  slippery.  Uniformity  of  wear  and  non- 
slipperiness  is  of  more  importance  in  a  paving  material  than 
hardness.  Unless  the  blocks  can  be  broken  with  smooth 
surfaces  they  cannot  be  laid  with  close  joints  and  will  chip,  giving 
the  pavement  a  cobble-stone  effect. 

Varieties  of  Materials  Used. — Granite  is  the  most  impor- 
tant rock  used  for  paving  blocks  in  the  United  States.  It  has 
the  required  properties  to  a  high  degree.  Granite  is  found 
pretty  generally  over  the  whole  country,  but  has  been  most 
largely  used  for  paving  in  the  Eastern  States.  Sandstone — 
Medina  sandstone  found  in  central  and  western  New  York, 
•while  not  as  hard  as  granite  has  proven  very  satisfactory  and 
durable;  pavements  of  more  than  fifty  years'  service  being 
known.  Minnesota  furnishes  the  Kettle  River  sandstone, 
which  is  extremely  gritty  and  somewhat  harder  than  Medina. 
It  breaks  well  and  can  be  laid  with  close  joints.  Colorado 
sandstone,  varying  in  color  from  red  to  gray,  is  another  popular 
stone  for  paving.  It  is  hard  and  tough  and  wears  well  and 
uniformly;  does  not  become  slippery  and  is  so  strong  that  it 
will  not  easily  break  under  traffic.  Sioux  Falls  (South  Dakota) 
granite,  which  is  really  a  quartzite,  has  been  used  to  a  consider- 
able extent.  It  is  hard,  tough  and  strong,  but  is  difficult  to 
prepare  and  wears  slippery. 

1  A  cobble-stone  pavement  still  in  daily  use  at  Alexandria,  Va.,  is  said 
to  have  been  laid  in  1776. 


. 
CONSTRUCTION   OF  STONE   BLOCK   PAVEMENTS      227 

Specifications. — The  American  Society  for  Municipal  Im- 
provements specifies  that  the  "blocks  shall  be  medium  grained 
granite,  showing  an  even  distribution  of  constituent  materials, 
of  uniform  quality,  structure  and  texture,  without  seams,  scales 
or  disintegration,  free  from  an  excess  of  mica  or  feldspar." 
For  heavy  traffic  the  specifications  require  a  toughness  of  not 
less  than  9,  and  a  French  coefficient  of  wear  of  not  less  than  1 1  ; 
for  medium  traffic,  7  and  8  respectively.  Tests  to  be  made 
according  to  the  methods  described  in  Bulletin  44,  Office  of 
Public  Roads,  U.  S.  Dept.  of  Agriculture. 

The  same  organization  gives  this  stipulation  for  sandstone 
paving  blocks:  "  shall  be  sound,  hard  sandstone,  free  from 
clay,  seams  or  defects  which  would  injure  them  for  paving  pur- 
poses, of  uniform  quality  and  texture." 

These  specifications  give  extreme  dimensions  as  follows: 
Granite — length,  8  to  12  inches  on  top;  width  3^  to  4J  inches 
on  top;  depth,  4f  to  5J  inches.  A  slightly  shallower  and 
narrower  block  may  be  specified  when  the  French  coefficient 
will  warrant.  Sandstone — length,  8  to  10  inches  on  top;  width, 
3f  to  6  inches  on  top;  depth,  4|  to  5J  inches. 

Recut  and  redressed  blocks  may  be  used  provided  they 
"  comply  with  the  specifications  for  the  quality  of  stone,  as 
required  for  new  blocks.  The  dimensions  may  be  varied, 
depending  upon  the  size  of  the  old  blocks  which  .are  to  be 
redressed,  and  the  character  of  the  pavement  which  it  is  sought 
to  obtain." 

Construction. — Upon  a  stable  foundation  about  2  inches  of 
sand  is  spread.  Into  this  cushion  the  blocks  are  individually 
bedded  by  hand,  using  a  stone  mason's  or  bricklayer's  hammer 
with  an  adz-shaped  peen  to  crowd  the  sand  under  the  block  until 
its  upper  side  is  in  line  with  the  street  surface.  The  blocks  are 
usually  laid  at  right  angles  to  the  street,  but  occasionally, 
especially  in  intersections,  are  placed  diagonally.  Joints  should 
always  be  broken,  the  minimum  lap  being  3  inches.  After 
laying,  the  blocks  are  rammed  to  bring  them  to  a  firm  bed  and 
true  surface.  The  fillers  used  are  either  sand,  grout  or  bitumi- 
nous materials.  If  sand,  it  should  be  very  dry  in  order  that  it 


228     BRICK,  STONE,  WOOD,  AND  OTHER  BLOCK  ROADS 

may  run  easily  into  the  joints  and  thoroughly  fill  them.  The 
joints  may  be  left  about  J  inch  wide  when  sand  is  used  for  filling. 
Cement  grout  is  applied  in  the  same  manner  as  already  described 
for  brick  paving;  when  asphalt  or  tar  pitch  is  used  the  joints 
should  be  as  close  as  it  is  possible  to  make  them.  The  pitch 
is  heated  and  poured  from  conical  or  from  sprinkler  shaped  cans. 
In  some  cases  the  joint  has  been  left  wide  and  first  filled  with 
gravel,  the  voids  then  being  filled  with  hot  pitch.  Or  a  mastic 
may  be  made  of  pitch  and  sand  and  forced  into  the  joint. 
Grouting  makes  a  solid  pavement,  but  one  more  noisy  than  a 
pitch  filled.  If  grout  is  used,  expansion  joints  as  in  brick 
pavements  should  be  provided. 

Small  and  Recut  Blocks. — Old  blocks  which  have  become 
"  turtle  backed  "  may  sometimes  be  taken  up,  recut,  and  used 
on  those  streets  where  the  traffic  is  moderate.  In  Europe 
small  blocks  more  or  less  cubical  in  form,  varying  from  2J  to  4 
inches  in  size,  are  laid  in  circular  arcs  of  small  radii,  something 
like  the  stitching  in  an  old-fashioned  quilt.  Thus  very  few 
of  the  joints  are  parallel  to  any  lane  of  traffic.  The  blocks 
'themselves  are  broken  to  size  by  a  machine  which  is  said  to  do 
the  work  very  rapidly.  In  England  this  pavement  is  known  as 
the  Durax,  while  a  similar  pavement  in  Germany  is  called 
the  Kleinpflaster. 

WOOD  BLOCK  PAVEMENT 

Wood  blocks  impermeated  with  coal  tar  creosote  make  an 
excellent  road  material.  They  are  durable,  smooth,  sanitary 
and  noiseless.  The  wood  fiber  at  the  top  of  the  block  "  brooms  " 
down  under  the  traffic,  forming  a  nap  or  carpet  which  is  elastic 
and  resilient,  thus  decreasing  further  wear  on  the  pavement  as 
well  as  lessening  jar  and  consequent  injury  to  the  vehicles 
(Fig.  128).  Wood  blocks  are  especially  adaptable  for  bridge 
covering,  and  for  places  where  noise  is  objectionable.  The 
cost  only  has  prevented  this  type  of  pavement  being  used  more 
extensively. 

Wood,  Varieties  Used. — A  reasonably  hard  and  tough  wood 
is  desirable,  Long-leaf  yellow  pine  is  preferred.  But  short- 


WOOD  BLOCK  PAVEMENT  229 

leaf  pine,  Norway  pine,  black  gum,  tamarack,  and  Douglas  fir 
are  American  woods  used.  Any  wood  of  uniform  texture  having 
a  crushing  strength  of  8000  pounds  or  more  per  square  inch, 
and  susceptible  to  impregnation  by  creosote,  would  make  good 
paving  blocks.  However,  a  real  hard  wood  might  wear  slip- 
pery; this  is  said  to  be  the  tendency  with  long-leaf  yellow  pine. 
Preparation. — The  timber  is  first  sawed  into  planks  and 
dressed  so  that  the  width  of  the  plank  equals  the  required 
length  of  the  block,  and  the  thickness  of  the  plank,  the  width 
of  the  block.  It  is  then  cross-sawed  into  short  lengths  equal  to 
the  depth  of  the  block.  The  ordinary  sizes  of  the  completed 
blocks  are:  Length,  from  5  to  10  inches;  width,  3  to  4  inches; 
depth,  3J  to  4  inches.  The  width  should  be  greater  or  less 


FIG.  128.— Showing  Wear  of  Wood  Blocks. 

than  the  depth  by  at  least  J-inch  to  insure  their  being  laid  with 
fibers  vertical.  In  the  same  job,  or  a  definite  portion  of  it  such 
as  a  city  block,  the  dimensions  for  depth  and  width  should  not 
vary  more  than  1/16  inch. 

Treatment. — The  properly  prepared  blocks  are  placed  in  a 
cylinder  or  a  tank  which  can  be  hermetically  closed.  They 
may  be  run  in  on  small  cars  and  after  treatment  drawn  out,  or 
conveyed  by  machinery  directly  from  the  block  saw  to  the  tank 
and  withdrawn,  after  treatment,  by  gravity.  The  tank  being 
closed  the  blocks  are  sterilized  by  live  steam  under  a  pressure 
of  at  least  30  and  not  more  than  50  pounds  per  square  inch,  for 
a  period  of  at  least  three  hours  and  not  to  exceed  seven  hours, 
and  a  temperature  between  250^  and  280°  F.,  as  the  condition 
of  the  wood  and  the  season  of  the  year  demands.  The  object 
of  steaming  is  to  drive  off  the  surplus  moisture  if  the  wood  is 


230     BRICK,  STONE,  WOOD,  AND  OTHER  BLOCK  ROADS 

t 

green,  to  add  moisture,  if  the  wood  is  too  dry,  and  partially  to 
coagulate  the  albumen  of  the  sap  thus  decreasing  the  hygro- 
scopicity  of  the  wood. 

After  steaming  air  pumps  create  a  partial  vacuum  (at  least 
24  inches)  in  the  tank  drawing  the  steam  and  air  from  the  heated 
wood.  Creosote — dead  oil  of  coal  tar  or  coal  tar  products — 
at  a  temperature  of  180  to  200°  F.,  is  then  allowed  to  flow  into 
the  tank  and  forced  and  maintained  under  sufficient  pressure 
to  impregnate  the  blocks  with  the  required  amount  of  creosote. 
Eighteen  pounds  per  cubic  foot  is  ordinarily  specified,  although 
20  pounds  is  sometimes  used,  and  in  Europe  as  low  as  10  pounds. 
The  excess  of  creosote  oil  in  the  tank  is  then  withdrawn,  the 
blocks  drained  and  prepared  for  shipment. 

Tests. — The  blocks  ready  for  use  should  not  absorb  more 
than  4J  per  cent  of  their  dry  weight  after  being  heated  at  100°  F. 
during  twelve  hours  and  then  placed  under  water  twelve  hours. 
The.y  must  stand  also  the  indentation  test  made  by  a  die  1  inch 
square  pressed  against  the  end  of  the  fibers  with  a  pressure  of 
8000  pounds  for  one  minute.  The  indentation  must  be  less 
than  \  inch. 

Laying. — The  foundation  is  preferably  prepared  by  sprin- 
kling the  concrete  with  water  and  distributing  over  it  a  layer  of 
mortar  at  least  \  inch  thick,  composed  of  one  part  Portland 
cement  and  three  parts  sand,  and  the  same  struck  off  to  a 
smooth  surface.  The  blocks  are  laid  immediately  upon  the 
mortar  bed  with  close  joints,  usually  at  right  angles  to  the 
curbs,  so  that  they  break  joints  with  a  lap  of  at  least  3  inches. 
Closure  or  end  blocks  should  be  at  least  3  inches  long.  After 
a  few  rows  of  blocks  have  been  laid  they  are  gently  rammed 
and  rolled  to  a  firm  bearing  and  uniform  surface. 

Filling. — As  in  the  case  of  brick  and  stone  block  pavements 
there  is  a  difference  of  opinion  as  to  what  constitutes  the  best 
filler.  Some  prefer  dry  sand  while  others  prefer  pitch.  Asphalt 
and  refined  tar  are  both  used.  Adherents  of  the  sand  filler 
claim  it  prevents  or  at  least  mitigates  the  nuisance  of  "  bleed- 
ing "  by  absorbing  the  surplus  oil  exuded  on  a  warm  day.  The 
bituminous  filler  is  claimed  to  prevent  the  penetration  of  water 


BITUMINOUS   AND   BITUMINIZED   BLOCKS  231 

into  the  pavement  with  consequent  swelling  and  heaving  of  the 
blocks.  The  character  of,  and  methods  of  applying  the  fillers 
are  practically  the  same  as  explained  for  brick  blocks. 

Expansion  Joints. — For  wide  streets  expansion  joints  are 
provided  between  the  wood  blocks  and  the  curb  of  such  thick- 
ness as  may  be  required,  to  l\  inches,  filled  with  pitch.  These 
are  unnecessary  when  a  bituminous  filler  is  used. 

Bituminous  blocks,  to  a  limited  extent,  have  been  used  for 
rural  roads.  These  are  made  in  the  factory  by  a  suitable 
mixture  of  stone,  sand  and  bituminous  cement,  hauled  to  the 
road  and  laid  on  the  concrete  foundation.  They  require  no 
filling,  as  the  joints  under  a  roller  or  under  traffic  soon  make  up 
and  the  blocks  become  practically  cemented  together  into  one 
continuous  surface.  The  exact  mixture  must  be  determined 
after  an  investigation  of  the  materials  to  be  used,  but  is  some- 
what similar  to  the  "  Topeka  "  specification  for  asphalt  con- 
crete (see  also  Chapter  XIII,  p.  308). 

Bituminized  brick  are  made  by  treating  common  brick  with 
asphalt  or  tar  under  pressure.  The  brick  are  ordinary  size 
and  should  absorb  from  6  to  12  per  cent  of  water  in  forty-eight 
hours'  immersion.  It  is  recommended  that  the  crushing  strength 
be  3500  pounds  per  square  inch.  The  brick  are  loaded  on  cars 
which  are  then  run  into  pre-heating  chambers,  the  interior  of 
which  are  kept  at  400°  F.,  until  the  bricks  have  been  freed  from 
moisture  and  have  expanded.  In  from  two  to  four  hours'  time 
they  are  ready  for  treatment  in  cylindrical  steel  tubes  about  6 
feet  in  diameter  and  36  feet  long  capable  of  withstanding  a 
pressure  of  200  pounds  per  square  inch.  The  door  is  closed,  the 
interior  temperature  raised  to  350°.  A  25-inch  vacuum  is 
produced  and  retained  about  one  hour  by  suitable  apparatus. 
Hot  asphalt,  350°,  is  then  admitted  to  the  chamber,  care  being 
taken  to  maintain  the  vacuum  until  all  bricks  have  been  cov- 
ered. The  valves  are  then,  reversed  and  a  pressure  of  160 
pounds  per  square  inch  applied  to  the  hot  contents.  Surplus 
asphalt  is  then  forced  out  of  the  chamber  and  the  brick  cooled,  a 
pressure  of  160  pounds  per  square  inch  being  maintained  until 
this  is  accomplished. 


232     BRICK,  STONE,  WOOD,  AND  OTHER  BLOCK  ROADS 

Rattler  tests  show  a  very  small  percentage  of  wear.  The 
bricks  take  up  by  this  process  about  5  to  10  per  cent  of  bitumen. 
Their  durability  in  the  road  has  not  yet  been  determined.  The 
special  claim  for  the  material  is  that  it  can  be  produced  wherever 
asphalt  and  a  good,  uniform  common  brick  can  be  secured.  If 
so,  a  cheap  pavement  may  be  provided  for  those  sections  of  the 
country  where  other  approved  road  materials  are  scarce. 


CHAPTER  XI 
CONCRETE  ROADS 

THE  deleterious  effect  of  automobile  traffic  on  waterbound 
macadam  caused  road  men  to  seek  for  a  stronger  binder  than 
stone-dust.  They  very  naturally  turned  to  Portland  cement. 
Has  Portland  cement  concrete  sufficient  resilience  to  withstand 
the  impact  of  traffic;  will  it  crack  and  disintegrate  under  the 
action  of  the  weather?  These  are  questions  that  no  laboratory 
test  can  determine;  experience  is  the  only  absolute  criterion. 
But  notwithstanding  that  these  questions  have  not  been  fully 
answered,  the  building  of  concrete  roads  has  gone  on  apace. 
Each  year's  output  shows  great  increase  over  the  preceding. 
While  defects  have  developed,  a  study  of  these  defects  has 
shown  that  a  closer  inspection  of  materials  and  better  methods 
of  grading,  mixing  and  laying  will  soon,  if  they  have  not  already, 
overcome  them. 

A  concrete  road  is  one  whose  wearing  surface  is  composed 
of  hydraulic  cement  concrete.  The  foundation  course,  if  there 
be  one,  is  usually  also  of  concrete,  making  truly  a  monolithic 
construction. 

MATERIALS  l 

Cement. — For  concrete  roads  only  Portland  cement  such  as 
will  pass  the  specifications  of  the  American  Society  for  Testing 
Materials  should  be  used.2  These  are  as  follows: 

^ee  "Specifications  and  Recommended  Practice"  of  the  National 
Conference  on  Concrete  Road  Building,  Chicago,  1914. 

2  For  a  completer  statement  of  the  specifications  and  methods  of  making 
the  tests  aee  "A.  S.  T.  M.  Standards,  1918,"  page  503. 

233 


234 


CONCRETE   ROADS 


SPECIFICATIONS 

1.  Portland  cement  is  the  product  obtained  by  finely  pulverizing  clinker 
produced  by  calcining  to  incipient  fusion,  an  intimate  and  properly  pro- 
portioned mixture  of  argillaceous  and  calcareous  materials,  with  no  addi- 
tions subsequent  to  calcination  excepting  water  and  calcined  or  uncalcined 
gypsum. 

I.  CHEMICAL  PROPERTIES 

2.  The  following  limits  shall  not  be  exceeded: 

Loss  on  ignition,  per  cent 4 . 00 

Insoluble  residue,  per  cent 0 .85 

Sulphuric  anhydride  (SO3),  per  cent 2 .00 

(MgO),  per  cent 5.00 


II.  PHYSICAL  PROPERTIES  AND  TESTS 

3.  The  specific  gravity  of  cement  shall  be  not  less  than  3.10  (3.07  for 
white  Portland  cement) .     Should  the  test  of  cement  as  received  fall  below 
this  requirement  a  second  test  may  be  made  upon  an  ignited  sample.     The 
specific  gravity  test  will  not  be  made  unless  specifically  ordered. 

4.  The  residue  on  a  standard  No.  200  sieve  shall  not  exceed  22  per  cent 
by  weight. 

5.  A  pat  of  neat  cement  shall  remain  firm  and  hard,  and  show  no  signs 
of  distortion,  cracking,  checking,  or  disintegration  in  the  steam  test  for 
soundness. 

6.  The  cement  shall  not  develop  initial  set  in  less  than  forty-five  min- 
utes when  the  Vicat  needle  is  used  or  sixty  minutes  when  the  GiUmore 
needle  is  used.     Final  set  shall  be  attained  within  ten  hours. 

7.  The  average  tensile  strength  in  pounds  per  square  inch  of  not  less 
than  three  standard  mortar  briquettes  (see  Section  51)  composed  of  one 
part  cement  and  three  parts  standard  sand,  by  weight,  shall  be  equal  to  or 
higher  than  the  following: 


Age  at  Test, 
days 

Storage  of  Briquettes 

Tensile 
Strength, 
Ib.  per  sq.  in. 

7 
28 

1  day  in  moist  air,  6  days  in  water  
1  day  in  moist  air,  27  days  in  water  

200 
300 

8.  The  average  tensile  strength  of  standard  mortar  at  twenty-eight 
days  shall  be  higher  than  the  strength  at  seven  days. 


AGGREGATES  235 

III.  PACKAGES,  MARKING  AND  STORAGE 

9.  The  cement  shall  be  delivered  in  suitable  bags  or  barrels  with  the 
brand  and  name   of  the  manufacturer  plainly  marked  thereon,   unless 
shipped  in  bulk.     A  bag  shall  contain  94  pounds  net.     A  barrel  shall  con- 
tain 376  pounds  net. 

10.  The  cement  shall  be  stored  in  such  a  manner  as  to  permit  easy 
access  for  proper  inspection  and  identification  of  each  shipment,  and  in  a 
suitable  weather-tight  building  which  will  protect  the  cement  from  damp- 
ness. 

IV.  INSPECTION 

11.  Every  facility  shall  be  provided  the  purchaser  for  careful  sampling 
and  inspection  at  either  the  mill  or  at  the  site  of  the  work,  as  may  be  spe- 
cified by  the  purchaser.     At  lease  ten  days  from  the  time  of  sampling  shall 
be  allowed  for  the  completion  of  the  seven-day  test,  and  at  least  thirty-one 
days  shall  be  allowed  for  the  completion  of  the  twenty-eight  day  test.     The 
cement  shall  be  tested  in  accordance  with  the  methods  hereinafter  pre- 
scribed.    The  twenty-eight  day  test  shall  be  waived  only  when  specifically 
ordered. 

V.  REJECTION 

12.  The  cement  may  be  rejected  if  it  fails  to  meet  any  of  the  require- 
ments of  these  specifications. 

13.  Cement  shall  not  be  rejected  on  account  of  failure  to  meet  the 
fineness  requirement  if  upon  retest  after  drying  at  100°  C.  for  one  hour  it 
meets  this  requirement. 

14.  Cement  failing  to  meet  the  test  for  soundness  in  steam  may  be 
accepted  if  it  passes  a  retest  using  a  new  sample  at  any  time  within  twenty- 
eight  days  thereafter. 

15.  Packages  varying  more  than  5  per  cent  from  the  specified  weight 
may  be  rejected;  and  if  the  average  weight  of  packages  in  any  shipment, 
as  shown  by  weighing  fifty  packages  taken  at  random,  is  less  than  that 
specified,  the  entire  shipment  may  be  rejected. 

AGGREGATES 

Fine  Aggregate. — This  may  be  either  sand,  or  stone  screen- 
ings less  than  J-inch  in  diameter.  It  should  be  hard,  approx- 
imately as  hard  as  flint  or  quartz,  tough,  dense,  and  free  from 
loam,  clay,  sticks,  or  organic  matter.  Siliceous  quartz  is  prefer- 
able although  sands  from  any  durable  rock  may  be  used. 
Sharpness  is  no  longer  considered  a  requisite.  While  sharp 
sands  give  a  little  greater  mechanical  bond  between  the  par- 


236 


CONCRETE  ROADS 


tides  the  voids  in  rounded  sand  is  less.  The  less  the  voids  the 
denser  the  mortar  and  denseness  is  considered  of  more  impor- 
tance than  the  small  mechanical  bond  that  may  ensue  from 
sharpness.  Likewise  since  denseness  is  desirable  a  graded 
mixture  of  grains  from  the  coarsest  to  the  finest  is  best.  If 
the  particles  could  be  carefully  laid  up  together  like  bricks  in  a 
house,  some  particular  uniform  size  would  be  most  convenient, 
but  in  a  random  mixture  the  best  results  seem  to  come  from  a 
regular  grading  of  the  grain  sizes.  A  granulometric  or  sieve 
analysis  will,  therefore,  give  an  indication  of  the  value  of  the 
sand  for  mortar.  A  first  class  sand  for  concrete  is  coarse, 

Sieve    Numbers 


.10  .15 

Size  of  Sieve  Opening,  Inches 

FIG.  129. — Mechanical  Analysis  of  Sand  Curves. 

I.  A  Platte  River  sand  (medium  fine). 
II.  Joliet,  111.,  limestone  screenings  (coarse  sand). 
III.  An  Illinois  bank  sand  (fine). 

that  is,  one  in  which  not  more  than  15  to  20  per  cent  will 
pass  a  No.  50  sieve,  and  not  more  than  2  per  cent  will  pass  a 
No.  100  sieve.  Cement  will  not  adhere  as  well  to  some  sands 
as  to  others.  Sands  should  then  show  when  mixed  into  a  mor- 
tar in  the  proportions  of  1  cement  to  3  sand,  by  weight,  a  tensile 
strength  equal  to  that  given  by  standard  Ottawa  sand  with  a 
like  mixture.  Dust  on  the  sand  may  prevent  its  adhering; 
washing  will  remove  it.  Careful  washing  may  also  remove 
mica,  which  occurs  in  small  flakes,  as  well  as  k>am,  clay  or 
sticks.  As  previously  stated,  coarse  sand  has  less  surface  area 
per  unit  of  weight  than  fine  sand.  If  each  grain  were  a  sphere 
it  would  be  easy  to  calculate  the  relative  areas.  The  total  area 


MECHANICAL  ANALYSIS  OF  SAND 


237 


of  a  given  weight  of  No.  300  sand  would  be  about  nineteen  times 
as  much  as  the  area  of  the  same  weight  of  No.  10  sand.  Con- 
sequently it  would  require  considerably  more  cement  to  coat 
the  No.  100  sand  than  it  would  to  coat  the  No.  10  sand.  There 
is  also  a  mechanical  stability  due  to. the  coarser  material.  Fig. 
129  shows  plots  of  the  mechanical  analyses  of  three  sands. 

Graded  Sand. — Fuller's  l  experiments  for  concrete  indicate 
that  for  cement,  sand  and  stone  the  curve  should  closely  approx- 
imate a  parabola,  or,  perhaps,  with  most  materials  a  straight 
line  combined  with  an  ellipse.  The  curves  drawn  in  Fig.  130 


.10  .15  .20  .25 

Size  of  Sieve  Openings, 

FIG.  130.— Well,  graded  Sands. 

I.  Well-graded  coarse  sand. 
II.   Well-graded  medium  sand. 

III.  Well-graded  fine  sand. 

IV.  Crusher-run  broken  stone. 

show  average  values  for  medium  sand  and  coarse  sand,  graded 
between  the  No.  100  sieve  and  J-inch  screen.  However,  with 
medium  and  fine  natural  sands,  there  is  usually  not  so  much  of 
the  coarser  grains  and  the  curve  will  reach  the  100  per  cent  line 
at  the  No.  10  or  No.  8  sieve  sizes.  It  is  hardly  worth  while  to 
attempt  a  very  close  grading  to  any  standard  until  that  standard 
has  been  better  established  than  at  the  present  time.  Perhaps 
one  or  two  sieves  will  furnish  sufficient  information  for  most 
jobs.  A  direct  test  for  strength  with  the  particular  cement 

1  Taylor  and  Thompson's  "Concrete,  Plain  and  Reinforced,"  Wiley 
&  Sons,  New  York.  "Laws  of  Proportioning  Concrete,"  by  W.  B.  Fuller 
and  S.  E,  Thompson,  Transactions  Am.  Soc.  Civ,  Eng,,  voL  59,  1907. 


238 


CONCRETE  ROADS 


to  be  used  is  the  best  criterion.  For  average  use  it  may,  how- 
ever, be  stated  that  results  within  the  following  limits  should  be 
obtained : 

CLASSES  OF  SAND 


No.  1 

No.  2 

No.  3 

Specific  gravity,  not  less  than 

2  6 

2  6 

2  6 

Voids,  not  more  than  per  cent 

33 

35 

38 

Suspended  matter,  not  more  than  per  cent  

2 

6 

8 

Through  No.  100  sieve,  not  more  than  per  cent. 

10 

15 

25 

Through  No.  50  sieve,  not  more  than  per  cent 

40 

45 

95 

Through  No.  30  sieve,  not  more  than  per  cent 

50 

60 

98 

Through  No.  20  sieve,  not  more  than  per  cent. 

60 

80 

100 

3  :  1  Tensile  strength  compared  with  3  :  1  mor- 

tar made  of  Ottawa  sand,  per  cent. 

100 

90 

80 

No.  1  sand  is  a  concrete  sand.  No.  2  sand  when  used  for  con- 
crete requires  some  additional  coarser  material;  this  may  come 
from  the  stone  which,  if  this  sand  is  used,  should  include  all 
fine  material  from  the  crusher  except  that  which  will  not  pass  a 
No.  8  sieve.  No.  3  sand  is  too  fine  for  cgncrete,  but  may  be 
used  for  grouting  brick  paving,  for  plastering  where  smoothness 
is  desired,  or  for  sheet  asphalt  pavements. 

Coarse  Aggregate. — A  tough,  hard  stone  is  best,  but  in  many 
sections  of  the  country  the  medium  grades  must  be  used.  The 
stone  may  be  tested  by  the  Duval  abrasion  machine.  A 
coefficient  of  wear  of  not  less  than  12  is  desirable.  This  will 
allow  the  better  grade  of  limestones.  The  stone  should  be  clean 
and  show  durability  as  noted  from  outcroppings  at  the  quarry. 
It  should  be  free  from  flat  or  elongated  pieces  and  from  vege- 
table or  other  deleterious  matter.  It  should  be  graded  in  size 
and  all  should  be  retained  on  a  J-inch  screen. 

Water. — Water  should  be  clean,  free  from  oil,  acid,  alkali  or 
vegetable  matter. 

Reinforcement. — All  reinforcement  should  develop  an  ulti- 
mate tensile  strength  of  not  less  than  70,000  pounds  per  square 


PROPORTIONING  CONCRETE  239 

inch  and  bend  180°  around  one  diameter  and  straighten  without 
fracture. 

Proportioning  Concrete. — The  National  Conference  on  Con- 
crete Road  Building  recommends  that  the  proportions  do  not 
exceed  5  parts  of  fine  and  coarse  aggregate  to  1  part  of  cement 
and  that  the  fine  aggregate  should  not  exceed  40  per  cent  of  the 
mixture  of  fine  and  coarse  aggregates. 

Proportioning  by  Arbitrary  Selection. — Arbitrary  propor- 
tions such  as  1  :  2  :  3,  1  :  2  :  4,  1  :  2  :  5,  etc.,  are  most  common 
and  least  scientific.  A  recommended  practice  is  to  use  at  first 
twice  as  much  coarse  aggregate  as  fine  aggregate  and  then  vary 
the  proportions  as  the  work  progresses.  If  there  is  a  harsh 
working  of  the  concrete  the  quantity  of  sand  may  be  lessened. 
If  stone  pockets  appear  and  it  is  difficult  to  fill  the  voids  more 
sand  should  be  used. 

Proportioning  by  Voids. — This  method  of  proportioning,  as 
explained  in  the  chapter  on  foundations,  requires  the  fine 
aggregate  to  a  little  more  than  fill  the  voids  of  the  coarse  and  the 
cement  to  a  little  more  than  fill  the  voids  of  the  fine  aggregate. 
It  is  necessary  because  of  the  swelling  of  the  bulk  to  take  from 
5  to  10  per  cent  excess  sand  and  from  5  to  10  per  cent  excess 
cement.  With  gravel  having,  say,  40  per  cent  voids,  use  45 
to  50  per  cent  sand.  Then  if  the  sand  is  to  be  twice  the  cement 
the  proportions  are 

1       part  stone 
.45  part  sand 
.22J  part  cement 

cement  :  sand  :  stone  =  . 22  J  :  .45  :  1.00 
=    1    :     2:4J 

If  the  sand  voids  are  32  per  cent,  say,  use  5  per  cent  more,  37. 
Then 

1         part  stone 
.45    part  sand 
.37  X  .45=   .16f  part  cement 
cement  :  sand  :  stone  =.16f  :  .45  :  1.00 
=  1       :  2.7  :  6 


240  CONCRETE  ROADS 

When  the  stone  is  uniformly  of  a  large  size  the  sand  may  be 
taken  equal  to  the  voids  or  only  slightly  in  excess  and  the  cement 
somewhat  in  excess  of  the  voids  in  the  sand,  5  to  15  per  cent  is 
recommended.  With  stone  having  40  per  cent  voids  and  sand 
of  32  per  cent  voids,  the  computation  is 

1       part  stone 
.40  part  sand 
(40+10)32  =  ,  .16  part  cement 

cement  :  sand  :  stone  =  .16  :  .40  :  1.00 
=    1  :  2.5  :  6.25. 

The  principal  error  of  this  method  of  proportioning  is  prob- 
able inaccuracies  in  determining  voids.  The  usual  method  is 
to  fill  a  vessel  with  the  stone  and  pour  water  in  to  fill  the  vessel. 
By  comparing  this  quantity  of  water  with  the  volume  of  the 
vessel,  the  percentage  of  voids  is  obtained.  In  the  concrete, 
however,  the  particles  of  sand  get  between  and  spread  the  pieces 
of  stone  apart  so  there  is  probably  a  greater  void  space.  Second, 
many  grains  of  sand  are  larger  than  the  void  spaces  between 
particles  of  stone  and  consequently  the  stones  cannot  come  into 
touch  and  there  is  again  swelling  in  bulk.  An  analysis  of  this 
subject  would  probably  lead  to  a  conclusion  that  two  sizes — a 
very  coarse  and  a  very  fine — are  requisite  for  densest  mortar. 
Feret  so  concluded  1  from  artificial  mixtures  of  sands  of  dif- 
ferent sizes.  His  experiments  lead  to  these  statements:  "  That 
a  sand  composed  of  4  parts  of  very  coarse  sand  (0.08 — 0.20 
inch  diameter)  to  1  part  of  very  fine  sand  (less  than  0.02 
inch  diameter)  makes  the  strongest  possible  mortar  of  1C  :  3S. 
That  the  strength  of  such  mortar  is  more  than  twice  as  much  as 
the  same  mortar  1C  :  3S  when  the  sand  is  composed  of  what 
is  commonly  regarded  as  "  coarse  sand  "  and  more  than  three 
times  as  strong  as  the  same  mortar  when  the  sand  is  very  fine. 
That  a  mixture  of  two  grades  of  sand  of  widely  different  sizes 

Johnson's  "Materials  of  Construction,"  Wiley  &  Sons,  New  York. 
Taylor  and  Thompson's  "Concrete  Plain  and  Reinforced,"  Wiley  &  Sons, 
New  York. 


MAXIMUM   DENSITY  CURVE 


241 


gives  a  great  deal  stronger  mortar  for  given  proportions  of 
sand  and  cement  than  does  any  particular  size  used  by  itself." 
Feret  would  use  as  coarse  aggregates  as  possible  leaving  in  the 
small  sizes  but  exclude  the  very  small  sizes.  The  present 
pracuice  is  toward  a  graded  mixture  as  giving  all  around  better 
results. 

Proportioning  Concrete  by  the  Maximum  Density  Curve. — 
The  theory  on  which  this  depends  is  (1)  "  With  the  same  per- 
centage of  cement  the  strongest  concrete  is  usually  that  in 
which  the  aggregate  is  proportioned  to  give  the  greatest  den- 
sity; (2)  with  the  same  aggregate  the  strongest  concrete  is  that 
containing  the  largest  percentage  of  cement  in  a  given  volume  of 
concrete,  the  strength  varying  in  proportion  to  this  percentage." 
Fuller  has  determined  that  the  maximum  density  curve  closely 
follows  a  curve  made  up  of  an  ellipse  and  a  straight  line.1  The 
data  for  plotting  the  curve  may  be  taken  from  the  following 
table:2 


Intersection 

Axe 

5  01 

of  Tangent 

Height  of 

Elli 

pse 

Materials 

with  Vertical 

Tangent 

at  Zero 

....  Point,.   _ 

Diameter 

a 

Mr 

Crushed  stone  and  sand  

28.5 

35.7 

0.150D 

37.4 

Gravel  and  sand.      ... 

26  0 

33  4 

0  164D 

35  6 

Crushed  stone  and  screenings  .  . 

29.0 

36.1 

0.147D 

37.8 

D  is  the  diameter  of  the  coarsest  stone. 

To  construct  the  curve,  lay  off  a  scale  along  the  F-axis, 
Fig.  130a,  to  represent  the  percentages  passing  the  sieves;  and 
a  scale  along  the  X-axis  to  represent  the  sieve  openings  or  size 
of  grains.  Draw  a  straight  line,  AB,  from  A.t  the  "  intercep- 

1  "Laws  of  Proportioning  Concrete,"  by  W.  B.  Fuller  arid  S.  E.  Thomp- 
son, Trans.  A.  S.  C.  E.,  Vol.  59,  1907. 

2  Taylor  and  Thompson's  "Concrete  Plain  and  Reinforced,"  2d  Edition, 
Wiley  &  Sons,  New  York. 


242 


CONCRETE  ROADS 


tion  of  tangent  with  vertical  at  zero,"  as  given  in  the  table, 
to  By  which  is  the  point  (D,  100).  Draw  the  axes  of  the 
ellipse  through  the  point  C,  where  x=  1/10Z),  and  y  =  7.  Draw 
in  the  ellipse  by  any  of  the  standard  methods;  the  trammel 


(D, 

100) 

^ 

^ 

8 

ftO 

^ 

fn 

^ 

^^ 

70 

fu 

^ 

£   CC 

- 

^ 

** 

•g      50 

^ 

^ 

>" 

3°4 

/ 

! 

\ 

-4- 

-  — 

\ 

/ 

| 

IT 

.10    .20  .30  .40    .50    .GO    .70  .80   .90  1.001.101.20 
Diameter  of  Steve  Openings 

FIG.  —  130a.  —  Method  of  Constructing  the  Fuller-Johnson  Maximum 
Density  Curve. 

method  is  recommended.  Mark  off  on  a  small  card  KL  equal 
to  the  horizontal  semi-axis,  and  KM  equal  to  the  vertical 
semi-axis  of  the  ellipse.  Rotate  the  card  about  C  so  that  the 


L'  A' 


w> 


J, 


40 


20 


0 


20 


40 


60 


SO 


100 


0  N  C     L  M 

FIG.  1306. — Diagrammatic  Sieve  Analysis  Curves. 

point  L  will  always  follow  the  vertical  axis  and  M  the  hori- 
zontal axis;  the  point  K  will  describe  the  ellipse. 

A  Mathematical  Analysis  of  Proportioning. — The  following 
analysis,  developed  by  the  author,  will  not  only  apply  to  pro- 
portioning concrete,  but  to  any  other  mixture  in  which  there 


COMBINING  TWO  INGREDIENTS  243 

is  a  predetermined  ideal  sieve-analysis  curve.  It  has  been 
successfully  used  in  proportioning  sheet  asphalt  mixtures.  It 
can,  of  course,  be  used  with  the  author's  straight-line  method 
of  plotting  described  in  a  previous  chapter. 

Having  drawn  the  mechanical  analysis  curves  of  the  several  ingre- 
dients and  decided  on  an  "ideal"  curve  for  the  mixture,  the  process  of 
proportioning  is  one  of  "alligation  medial"  or  it  is  analogous  to  the  reverse 
operation  of  finding  the  centroid  in  mechanics. 

Fig.  1306  shows  diagrammatic  sieve  analysis  curves  for  two  ingredients, 
OAB  for  I,  and  OCB  for  II.  Suppose  it  is  desired  to  make  a  mixture  of 
these  two  ingredients  so  that  the  sieve  N  (vertical  NN')  will  separate  the 
mixture  into  two  portions  such  that  24  per  cent  will  pass  and  76  per  cent  be 
retained  on  that  sieve.  It  will  be  noted  that  60  per  cent  of  I  is  finer  than 
(passes)  this  sieve  while  none  of  II  passes  the  sieve. 

Let  x  =  percentage  of  mixture  to  be  taken  from  1;^ 
and        y  =  percentage  of  mixture  to  be  taken  from  II. 

Then  zat60  =  60z 

?/at    0  =  0 

(x+y)  at  24  =  60z+0 
Algebraically 

(x+y)24  =  QOx 
but 

x+y  =  100 
Therefore 

2400  =  QOx 


?/  =  100-40  =  60. 

Suppose  the  sieve  M  (vertical  MM')  is  to  retain  20  per  cent  and  allow 
80  per  cent  to  pass.     As  before 

x  at  100 


(x+y)  at  80  = 
Algebraically 


and 

x+y  =  100 


244  CONCRETE  ROADS 

Solving  for  x  and  y 


Suppose  along  LL'  the  desired  mixture  is  to  have  60  per  cent  pass  the 
sieve. 

x  partsat90  =  90z 

y  parts  at  10  =  Wy 
(x+y)  at  60  =  90z+10?/ 


but, 


It  will  be  noticed  that  in  each  case  the  ratio  of  the  parts  taken  are 
inversely  proportional  to  the  distances  along  the  ordinate  from  the  point 
representing  the  desired  mixture,  indicated  on  the  diagram  by  the  small 
circles,  to  the  lines  representing  the  sieve  analyses.  Algebraically, 

For  sieve  N, 

x/y  =  NP/nP 
or 

x/x+y=NP/(NP+nP)  =NP/Nn 

x  =  (x+y)(NP/Nn)  =  IWNP/Nn 
and 

=  nP/(NP+nP)  =nP/Nn 


y  =  (x+y)(nP/Nn)  =  IWNP/Nn 
For  sieve  M, 

x/y  =  Qm/QM' 


For  sieve  L, 


COMBINING  TWO   INGREDIENTS  245 

This  last  is  a  general  expression  including  the  other  two  as  special  cases. 
The  values  of  x  and  y  in  either  case  are  easily  calculated  by  slide  rule. 

Application  to  Proportioning  Concrete. — The  National  Conference  rule 
quoted  is,  that  the  fine  aggregate  shall  not  exceed  40  per  cent  of  the  mix- 
ture of  fine  and  coarse  aggregate. 

Suppose,  then,  the  sieve  analysis  of 
the  sand  and  coarse  aggregate  to  have 
been  plotted,  Fig.  131. 

Put  the  point  R  at  40  on  the  sieve 
ordinate  separating  the  fine  from  the 
coarse  aggregate,  then  the  part  of  I  to 
be  taken  is  Rl  =  38  per  cent,  and  of  II. 
Rl'  =58  per  cent.  Check  by  substitut- 
ing in  the  formula:  FIG.  131 
z-100/B/fl' 

=  100  X  38/96  =  40  per  cent 
y  =  IQQRl'/ll' =60  per  cent. 

That  is  by  weight  the  quantities  of  sand  :  stone  =  40  :  60.  The  conference 
also  recommends  that  the  proportions  do  not  exceed  five  parts  of  fine  and 
coarse  aggregate  to  one  part  of  Portland  cement. 

cement  :  aggregate  =  1:5. 

But  the  five  parts  of  aggregate  are  divided  as  40  to  60. 

Sand  =40/100  of  5  =  2 

Stone  =  60/100  of  5=3. 
The  proportions  then  are 

Cement  :  sand  :  stone  =  1  :  2  :  3. 

These  proportions  will  in  practice  have  to  be  reduced  to  volumes  unless 

the  cement  sand  and  stone  have  approximately  the  same  specific  gravities. 

Let  the  specific  gravities  and  weights  per  cubic  foot  of  the  ingredients  be 

Cement 3 . 14         196  (one    sack) 

Sand „ 2.65         166 

Stone 2 . 60         162 

Since  the  volumes  are  inversely  proportional  to  the  specific  gravities  or 
the  weights 

cement  :  sand  :  stone  =  1:2:3.  by  weight 

=  1/3.14  :  2/2.65  :  3/2.60  by  volume 

=  1  :  2X3.14/2.65  :  3X3.14/2.60 
(By  slide  rule) 

=  1  :2.37  :361 


246 


CONCRETE   ROADS 


To  obtain  a  mixture  that  will  coincide  with  the  ideal  curve  at  any  number 
of  points. 

As  has  been  stated,  p.  241,  the  mechanical  or  sieve  analysis 
curve  for  maximum  density  closely  follows  a  curve  composed  of  an  ellipse 
and  a  straight  line.  Where  several  ingredients,  then,  are  to  be  mixed  the 
problem  is  to  obtain  a  mixture  which  will  approach  as  near  as  may  be  this 
"ideal"  curve.  The  method  given  may  be  used  to  secure  a  mixture  which 
will  fit  any  predetermined  curve. 

Consider  the  sieve  analysis  curves,  Fig.  132.  Let  q\,  q»,  q3,  q*,  .  .  . 
represent  the  percentage  (number  of  parts)  of  the  whole  mixture  to  be 
taken  of  the  ingredients  I,  II,  III,  IV,  .  .  .  respectively.  Let  pi  represent 
the  percentage  of  I  which  will  pass  a  given  sieve,  pz  the  percentage  of  II 
which  will  pass  the  same  sieve,  p3  of  III,  p*  of  IV  and  so  on;  and  P  repre- 
sent the  percentage  of  the  whole  mixture  that  will  pass  the  same  given 


II 


III 


IV 


0     .1     .2     .3 


.4     .5     .6     .7     .8    .9     1.0  1.1  1.2  1.3  1.4   1.6 
Size  of  Sieve  Opening 


FIG.  132.  —  Combining  Four  Ingredients. 

sieve.  Then  for  any  sieve  ordinate  an  equation  can  be  written  by  noting 
that  q  parts  of  I  of  which  p  will  pass  the  sieve  is  equal  to  pq  parts  of  the 
whole  mixture  passing  that  sieve.  Taking  the  parts  of  each  of  the  ingre- 
dients in  order: 

qi  parts  of  I  fineness  p\  =p\q\  parts  of  the  whole. 
qz  parts  of  II  fineness  p2  =  pzqt  parts  of  the  whole. 
<?3  parts  of  III  fineness  pz  =  p^qz  parts  of  the  whole. 
54  parts  of  IV  fineness  pt^piqi  parts  of  the  whole. 

The  whole  mixture  to  be  "ideal"  must  have  a  "fineness"  of  P,  that  is,  P 
per  cent  must  pass  the  given  sieve.  Therefore  the  statements  above  may 
be  expressed  algebraically. 


(1) 


PLOTTING   RESULTANT  CURVE  247 

When  all  the  ingredients  will  pass  the  largest  screen 

and 


(2) 


This  is  the  general  equation  to  be  used  in  proportioning  concrete  so  that 
the  density  curve  will  approach  the  ideal  curve. 

An  equation  of  this  kind  may  be  written  for  every  ordinate  of  the 
diagram.  When  there  are  n  ingredients,  n  of  these  equations  may  be 
taken  as  independent  equations  and  the  values  of  q  computed;  the  density 
curve  resulting  from  this  computation  will  agree  with  the  ideal  curve  at  n 
points. 

For  example,  using  Fig.  132,  first  writing  the  general  equation  in  the 
form 

.  .  .    =100P, 


there  results  for  the  ordinates  through 

0.1,      939i  =3200 

0.5,      100^+9592+3593  =5200 

0.8,      lOOg!  +  10092  +75^3  =6600 

1  .  5,  *     1009!  +  10092  +  10093  +  10094  =  10,000 

1  It  is  necessary  that  one  equation  be  taken  for  the  ordinate  where  the 
ideal  curve  meets  the  100  per  cent  line,  otherwise,  Sp  would  not  equal  100 
and  Equation  (2)  would  not  hold. 

And  so  on  for  as  many  ordinates  as  may  be  desired.  Using  these  four 
equations,  that  is,.  assuming  that  the  density  curve  is  to  coincide  with  the 
ideal  curve  on  the  ordinates  considered,  and  solving,  there  results,  omitting 
fractions, 

9i  =  34 

9z=  7 

93  =  34 

94  =  25 

Theoretically  a  solution  for  any  four  ordinates  is  possible;  practically 
the  values  thus  found  will  not  always  answer,  because  negative  quantities 
cannot  be  used.  The  small  value  of  92  here  indicates  that  the  ingredient  II 
might  be  omitted  without  great  detriment  to  the  mixture;  a  suggestion 
given,  also,  by  a  view  of  the  plot,  Fig.  132. 

Plotting  the  Curve.—  Substitute  the  calculated  or  selected  values  of 


248  CONCRETE   ROADS 

Qij  ?2,  <Zs,  <?4,  in  the  general  equation  for  as  many  ordinates  as  desired  and 
find  P.     For  example  (the  subscript  indicates  the  ordinate)  : 


P  =  -^(general  equation) 


_ 


100X34+67X7+8X34 
Po'3=  TOO" 

_  100X34  +  100X7+39X34  _ 

100 

100X34  +  100X7+94X34 
Pl'0=  ~T66~~ 

_100X34+100X7  +  100X34+35X25_ 
100 


A  curve  plotted  through  these  points  will  approximately  coincide  with 
the  "ideal"  curve.  It  will  also  show  wherein  other  ordinates  should  have 
been  used  to  determine  the  proportions  q;  or  how  the  values  of  q  may  be 
modified  to  fit  the  "ideal"  curve  better. 

PROPORTIONS  USED  IN  PRACTICE 

The  practice  of  the  last  few  years  is  toward  a  denser  and 
richer  mixture.  The  Standard  Specifications  of  the  "  American 
Concrete  Institute,"  1914,  state: 

"  The  concrete  shall  be  mixed  in  the  proportions  of  one 
bag  of  Portland  cement  to  not  more  than  2  cubic  feet  of  fine 
aggregate  and  not  more  than  3  cubic  feet  of  coarse  aggregate, 
and  in  no  case  shall  the  volume  of  fine  aggregate  be  less  than 
one-half  the  volume  of  coarse  aggregate.  A  cubic  yard  of 
concrete  in  place  shall  contain  not  less  than  1.7  barrels  (6.8 
bags  of  cement."  Calling  a  bag  of  cement  1  cubic  foot  the 
limiting  proportions  above  would  be 

cement  :  sand  :  stone  =  1:2:3 

These  proportions  apply  to  one-course  pavements  and  the 
upper  or  wearing  course  of  two-course  pavements.  Tiie  lower 


ABRAMS'   METHOD  OF  PROPORTIONING 


249 


course  of  a  two-course  pavement  may  have  concrete  of  the  pro- 
tions  of  "  one  bag  Portland  cement  to  not  more  than  2|  cubic 
feet  of  fine  aggregate,  and  not  more  than  4  cubic  feet  of  coarse 
aggregate."  That  is, 

cement  :  sand  :  stone  =  1  :  2 J  :  4. 

Abrams'  Fineness  Modulus  Method. — Abrams  has,  as  a 
result  of  a  number  of  years'  experimenting  and  approximately 
50,000  tests,  given  out  the  statement  that: 

"  Our  experimental  work  has  emphasized  the  importance 


70    80   90   100  110  120  130  140  150  160  170  180  190  200 
Water  Used -Percent  of  Quantity  Giving  Maximum  Strength 

FIG.  133. — Effect  of  Water'on  the  Strength  of  Concrete  (Abrams). 

C  (105  to  115)  is  about  the  proper  consistency  for  concrete  road  work.  With  the 
"sloppy"  concrete,  E  sometimes  used,  two-thirds  to  three-fourths  the  possible  strength 
of  the  concrete  is  lost. 

of  the  water  in  concrete  mixtures,  and  shown  that  the  water 
is,  in  fact,  the  most  important  ingredient,  since  very  small 
variations  in  the  water  content  produces  more  important  varia- 
tions in  the  strength  and  other  properties  of  concrete  than 
similar  changes  in  the  other  ingredients."  1 

Fig.  133  shows  what  Professor  Abrams  found  to  be  the  effect 

1  Bulletin  No.  1,  Structural  Materials  Research  Laboratory,  Lewis 
Institute,  Chicago,  "Design  of  Concrete  Mixtures,"  by  Duff  A.  Abrams, 
Professor  in  Charge.  A  series  of  bulletins  have  been  published  by  the 
Laboratory  on  the  results  of  researches  in  the  properties  of  concrete  and 
concrete  materials  carried  on  through  the  co-operation  of  Lewis  Institute 
and  the  Portland  Cement  Association,  Chicago. 


250  CONCRETE  ROADS 

of  water  on  the  strength  of  concrete.  The  vertical  distances 
represent  the  relative  strength  of  concrete,  expressed  as  a  per 
cent  of  the  maximum  which  can  be  secured  from  the  same 
mixture  of  cement  and  aggregates  with  varying  quantities  of 
water.  The  horizontal  distances  indicate  the  relative  quan- 
tity of  water  used  in  the  mix,  considering  the  amount  which 
gives,  the  maximum  strength  as  100  per  cent.  A  decrease  or 
an  increase  of  the  quantity  of  water  causes  the  strength  to  fall 
off  rapidly.  The  absolute  quantity  of  water  corresponding  to 
maximum  strength  of  concrete  will  vary  with  the  method  of 
handling  and  placing  an  over-watered  concrete.  Puddling, 
rodding,  tamping,  rolling,  vibration,  troweling,  or  the  applica- 
tion of  pressure  will  have  a  tendency  to  strengthen  the  con- 
crete. The  quantity  of  water  required  is,  according  to  Abrams, 
governed  by  (a)  the  condition  of  workability  of  concrete  which 
must  be  used  —  the  relative  plasticity  or  consistency;  (6)  the 
normal  consistency  of  the  cement;  and  (c)  the  size  and  grading 
of  the  aggregate  —  measured  by  the  fineness  modulus. 

Abrams'  investigations  lead  him  to  the  following  equation 
for  the  comparative  strength  of  concrete  and  water  content: 


(i) 


where  S  is  the  strength  of  the  concrete  and  x  the  ratio  of  the 
volume  of  water  to  the  volume  of  cement  in  the  batch.  A  and  B 
are  constants  whose  values  depend  on  the  quality  of  the  cement 
used,  the  age  of  the  concrete,  curing  conditions,  etc.  For  the 
conditions  under  which  Abrams'  tests  were  made  this  becomes 

14,000 
fr=    7x    •   .......    (2; 

Fig.  134  is  a  plot  of  this  curve  which  is  an  average  of  the  results 
of  tests  of  the  several  mixes. 

He  then  finds  the  following  relation  between  the  quantity 
of  water  for  given  proportions  and  conditions: 


ABRAMS'  METHOD  OF  PROPORTIONING 


251 


or  approximately, 
x  = 

where    x  represents  the  water  ratio 


(4) 


volume  of  water 
volume  of  cement' 


8000 


100  150  200  250  SCO 

Water  Ratio  to  Volume  of  Cement  ~-  X 


350 


400 


FIG.  134. — Relation  between  Strength  of  Concrete  and  Water  Content 

(Abrams) 
Twenty-eight-day  compression  tests  of  6  by  12-inch  cylinders.     (Series  83.) 

R,  the  relative  consistency  of  concrete  or  " workability 
factor."  Normal  consistency  requires  the  use  of  such 
a  quantity  of  mixing  water  as  will  cause  a  slump  of 
|  to  1  inch  in  a  freshly  molded  6  X  12-inch  cylinder  of 
about  1  :  4  mix  upon  withdrawing  the  form  by  a 
steady  upward  pull.  A  relative  consistency  of  1.10 
requires  the  use  of  10  per  cent  more  water  and  under 
above  conditions  will  give  a  slump  of  about  5  to  6 
inches. 

p,  the  normal  consistency  of  cement,  ratio  by  weight; 

m,  the  fineness  modulus  of  aggregate; 

a,  the  absorption  of  aggregate,  three  hours'  immersion; 

c,  the  moisture  contained  in  aggregate — ratio  volume  con- 
tained to  volume  of  aggregate. 


252 


CONCRETE   ROADS 


The  Fineness  Modulus  is  determined  by  a  sieve  analysis. 
The  sieves  used  are  the  Tyler  standard  in  which  the  clear  mesh- 
opening  of  each  sieve  is  just  double  that  of  the  preceding  one. 
The  sieve  analysis  is  expressed  in  terms  of  either  volume  or 
weight  as  the  percent  coarser  than  each  sieve.  The  fineness 
modulus  of  an  aggregate  is  defined  as  the  Sum  of  the  percentages 
given  by  the  sieve  analysis  divided  by  100.  The  following 
table  taken  from  the  bulletin  cited  gives  the  method  of  calcu- 
lating the  fineness  modulus : 

TABLE  I 
METHOD  OF  CALCULATING  FINENESS  MODULUS  OF  AGGREGATES 

The  sieves  used  are  commonly  known  as  the  Tyler  standard  sieves. 
Each  sieve  has  a  clear  opening  just  double  that  of  the  preceding  one. 

The  sieve  analysis  may  be  expressed  in  terms  of  volume  or  weight. 

The  fineness  modulus  of  an  aggregate  is  the  sum  of  the  percentages  given 
by  the  sieve  analysis,  divided  by  100. 


Sieve 
Size 

Size  of 
Square  Open- 
ing 

SIEVE  ANALYSIS  OF  AGGREGATES 
Per  Cent  of  Sample  Coarser  than  a  Given  Sieve 

Sand 

Pebbles 

Con- 
crete 
Aggre- 
gate 

(G)i 

in. 

mm. 

Fine 

(A) 

Medium 

(B) 

Coarse 
(C) 

Fine 
(D) 

Medium 

05) 

Coarse 

(F) 

100-mesh  

.0058 

.147 
.295 
.59 
1.17 
2.36 
4.70 
9.4 
18.8 
38.1 

82 
52 
20 
0 
0 
0 
0 
0 
0 

91 
70 
46 
24 
10 

: 

0 
0 

'97 
81 
63 
44 
25 
0 
0 
0 
0 

100 
100 
100 
100 
100 
86 
51 
9 
0 

100 

•100 

100 
100 
100 
95 
66 
25 
0 

100 
100 
100 
100 
100 
100 
86 
50 
0 

98 
92 
86 
81 
78 
71 
49 
19 
0 

48-mesh  

.0116 
.0232 
.046 
.093 
.185 
.37 
75 
1-5 

28-mesh  
14-mesh  
8-mesh  
4-mesh    

i-inch  
j-inch  

li-inch  
Fineness  modul 

1.54 

2.41 

3.10 

6.46 

6.86 

7.36 

5.74 

1  Concrete  aggregate  "G"  is  made  up  of  25  per  cent  of  sand  "B"  mixed  with  75 
per  cent  of  pebbles  "E."  Equivalent  gradings  would*be  secured  by  mixing  33  per  cent 
sand  "B"  with  67  per  cent  coarse  pebbles  "F";  .28  per  cent  "A"  with  72  per  cent 
"F,"  etc.  The  proportion  coarser  than  a  given  sieve  is  made  up  by  the  addition  of 
these  percentages  of  the  corresponding  size  of  the  constituent  materials. 


FINENESS   MODULUS 


253 


Maximum   Permissible    Values    of   Fineness   Modulus. — 

Practical  considerations  make  it  necessary  to  establish  upper 
limits  for  the  fineness  modulus  of  aggregates.  Professor  Abrams' 
table  for  these  values  follows: 

TABLE  II 

MAXIMUM  PERMISSIBLE  VALUES  OF  FINENESS  MODULUS  OF  AGGREGATES 


Mix 

Size  of  Aggregate 

Cem. 

0-28 

0-14 

0-8 

0-4 

0-3i 

o-i 

(M« 

0-f 

0-1 

o-H 

0-2.  I1 

0-3 

0-4* 

0-6 

Agg. 

in.1 

in. 

1-12 

1.20 

1.80 

2.40 

2.95 

3.35 

3.80 

4.20 

4.60 

5.00 

5.35 

5.75 

6.20 

6.60 

7.00 

1-9 

1.30 

1.85 

2.45 

3.05 

3.45 

3.85 

4.25 

4.65 

5.00 

5.40 

5.80 

6.25 

6.65 

7.05 

1-7 

1.40 

1.95 

2.55 

3.20 

3.55 

3.95 

4.35 

4.75 

5.15 

5.55 

5.95 

6.40 

6.80 

7.20 

1-6 

1.50 

2.05 

2.65 

3.303.65 

4.05 

4.45 

4.85 

5.25 

5.65 

6.05 

6.50 

6.90 

7.30 

1-5 

1.60 

2.15 

2.75 

3.45 

3.80 

4.20 

4.60 

5.00 

5.40 

.5.80 

6.20 

6.60 

7.00 

7.45 

1-4 

1.70 

2.30 

2.90 

3.60 

4.00 

4.40 

4.80 

5.20 

5.60 

6.00 

6.40 

6.85 

7.25 

7.65 

1-3 

1.85 

2.50 

3.10 

3.90 

4.30 

4.70 

5.10 

5.50 

5.90 

6.30 

6.70 

7.15 

7.55 

8.00 

1-2 

2.00 

2.70 

3.40 

4.20 

4.60 

5.05 

5.45 

5.90 

6.30 

6.70 

7.10 

7.55 

7.95 

8.40 

11 

2.25 

3.00 

3.80 

4.75 

5.25 

5.60 

6.05 

6.50 

6.90 

7.35 

7.75 

8.20 

8.65 

9.10 

1  Considered  as  "half -size"  sieves;  not  used  in  computing  fineness  modulus. 

For  mixes  other  than  those  given  in  the  table,  use  the  values  for 
the  next  leaner  mix. 

For  maximum  sizes  of  aggregate  other  than  those  given  in  the  table,  use 
the  values  for  the  next  smaller  size. 

Fine  aggregate  includes  all  material  finer  than  No.  4  sieve;  coarse  aggre- 
gate includes  all  material  coarser  than  the  No.  4  sieve.  Mortar  is  a  mix- 
ture of  cement,  water  and  fine  aggregate. 

This  table  is  based  on  the  requirements  for  sand-and-pebble  or  gravel 
aggregate  composed  of  approximately  spherical  particles,  in  ordinary 
uses  of  concrete  in  reinforced  concrete  structures.  For  other  materials 
and  in  other  classes  of  work  the  maximum  permissible  values  of  fineness 
modulus  for  an  aggregate  of  <a  given  size  is  subject  to  the  following  cor- 
rections : 

(1)  If  crushed  stone  or  slag  is  used  as  coarse  aggegate.  reduce  values  in 
table  by  0.25.  For  crushed  material  consisting  of  unusually  flat  or  elongated 
particles,  reduce  values  by  0.40. 

(2)  For  pebbles  consisting  of  flat  particles,  reduce  values  by  0.25. 

(3)  If  stone  screenings  are  used  as  fine  aggregate,  reduce  values  by  0.25. 

(4)  For  the  top  course  in  concrete  roads,  reduce  the  values  by  0.25.     If 
finishing  is  done  by  mechanical  means,  this  reduction  need  not  be  made. 

(5)  In  work  of  massive  proportions,  such  that  the  smallest  dimension  is 


254  CONCRETE  ROADS 

larger  than  ten  times  the  maximum  size  of  the  coarse  aggregate,  additions 
may  be  made  to  the  values  in  the  table  as  follows:  for  f-in.  aggregate  0.10; 
for  H-in.  0.20;  for  3-in.  0.30;  for  6-in.  0.40. 

Sand  with  fineness  modulus  lower  than  1.50  is  undesirable  as  a  fine 
aggregate  in  ordinary  concrete  mixes.  Natural  sands  of  such  fineness  are 
seldom  found. 

Sand  or  screenings  used  for  fine  aggregate  in  concrete  must  not  have  a 
higher  fineness  modulus  than  that  permitted  for  mortars  of  the  same  mix.' 
Mortar,  mixes  are  covered  by  the  table  and  by  (3)  above. 

Crushed  stone  mixed  with  both  finer  sand  and  coarser  pebbles  requires  no 
reduction  in  fineness  modulus  provided  the  quantity  of  crushed  stone  is  less 
than  30  per  cent  of  the  total  volume  of  the  aggregate. 

Steps  in  the  Design  of  Concrete  Mixtures.  —  The  following  is 
an  abstract  of  the  outline  of  procedure  given  in  the  bulletin  cited  : 

1.  Knowing  the  compressive  strength  required  of  the  concrete,  deter- 
mine by  reference  to  Fig.  134  the  maximum  water-ratio  which  may  be 
used.     A  given  water-ratio  can  be  secured  with  a  minimum  of  cement  if 
the  aggregate  is  graded  as  coarse  as  permissible. 

2.  Make  sieve  analyses  of  fine  and  coarse  aggregates,   using  Tyler 
Standard  sieves  of  the  following  sizes:    100,  48,  28,  14,  8,  4,  f,  f,  and  If 
inches.     Express  sieve  analyses  in  terms  of  percentages  of  material  by 
weight  (or  separate  volumes)  coarser  than  each  of  the  standard  sieves. 

3.  Compute  fineness  modulus  of  each  aggregate  by  adding  the  per- 
centages found  in  (2)  and  dividing  by  100. 

4.  Determine  the  "maximum  size"  of  aggregate  by  applying  the  fol- 
lowing rules:  If  more  than  20  per  cent  of  aggregate  is  coarser  than  any  sieve 
the  maximum  size  shall  be  taken  as  the  next  larger  sieve  in  the  standard 
set;   if  between  11  and  20  per  cent  is  coarser  than  any  sieve,  maximum 
size  shall  be  the  next  larger  "half  sieve";  if  less  than  10  per  cent  is  coarser 
than  certain  sieves  the  smallest  of  these  sieve  sizes  shall  be  considered,  the 
maximum  size. 

5.  From  Table  I  determine  the  maximum  value  of  fineness  modulus 
which  may  be  used  in  the  mix,  "kind  and  size  of  aggregate,  and  the  work 
unde.r  consideration. 

6.  Conipute  the  percentages  of  fine  and  coarse  aggregates  required  to 
produce  the  fineness  modulus  desired  for  the  final  aggregate  mixture  by 
applying  the  formula: 


where  P  is  the  percentage  of  fine  aggregate  in  the  total  mixture; 

A,  the  fineness  modulus  of  the  coarse  aggregate; 

B,  the  fineness  modulus  of  tke  final  aggregate  mixture; 

C,  the  fineness  modulus  of  the  fine  aggregate. 


DESIGN  OF  CONCRETE   MIXTURES 


255 


7.  With  the  estimated  mix,  fineness  modulus  and  consistency  enter 
Fig.  135  and  determine  the  strength  of  concrete  produced  by  the  combina- 
tion. If  the  strength  shown  by  the  diagram  is  not  that  required,  the 
necessary  readjustment  may  be  made  by  changing  the  mix,  consistency 
or  size  and  grading  of  the  aggregates. 

The  quantity  of  water  can  be  determined  from  Equation  (3)  or  ap- 
proximately from  Table  3. 

IMPORTANCE  NOTE. — It  must  be  understood  that  the  values  in  Fig.  135 
were  determined  from  compression  tests  of  6  X  12-inch  cylinders  stored 


1-6.5   - 


1-7 


.  90  1.00 1.10  1.20 1.30 1.401. 501.601.70 
Relative    Consistency 


FIG.  135.— Abrams'  Diagram  for  Designing  Concrete  Mixtures. 

for  twenty-eight  days  in  a  damp  place.  The  values  obtained  on  the  work 
will  depend  on  such  factors  as  the  consistency  of  the  concrete,  quality  of  the 
cement,  method  of  mixing,  handling,  placing  the  concrete,  etc.,  and  on  the 
age  and  curing  conditions. 

Strength  values  higher  than  given  for  relative  consistency  of  1.10 
should  seldom  be  considered  in  designing,  since  it  is  only  in  exceptional 
cases  that  a  consistency  drier  than  this  can  be  satisfactorily  placed.  For 
wetter  concrete  much  lower  strengths  must  be  considered. 

The  quantity  of  water  to  be  used  may  be  calculated  by 
Formula  (3)  or  taken  from  the  table  below,  which  is  calculated 


256 


CONCRETE   ROADS 


Abrams'  Table  of  Proportions  and  Quantities  for 
One  Cubic  Yard  of  Concrete 

Based  upon  laboratory  investigations,  using  approved  materials,  compres- 
sive  strength,  2S  days,  with  workable  plasticity,  6  by  12-inch  cylinders,  3,000 
pounds  per  square  inch. 


SUB 

mil;  «GGBtG«TES.  SCRECN  OPENINGS  PCR  INCH 

i 

T5,! 

0-28 

O-14 

0-8 

0-4 

0-H  In. 

iftl 

J 

I 

| 

] 

1 

! 

I 

J 

1 

I 

| 

! 

rp 

i 
IJ 

• 

N*4 

lent* 

••  3  < 

^rcMrti 

1 

196 

1  3 

24 

1 

16 

24 

1 

1.8 

23 

1 

1.75 

2.0 

52 

2.3 

59 

1 

Ul 

2.7 

.72 

OMbta 

N..4 

tmm 
bl 

?        rt 

1 
1  % 

13 

36 

2.7 

M 

1  7? 

1.6 

42 

26 

H 

1  72 

1.8 

46 

26 

66 

167 

2.0 

50 

2.5 

62 

1 

172 

2.S 

6S 

1.8 

• 

QuMtllMI 

•k.4 

Sow* 

»l'/j 

Ounttwi 

1 

:82 

i  ; 

t 

3.1 

54 

m 

16 

40 

32 

7^ 

ua 

1.7 

41 

3.1 

75 

16' 

2 
17 

3 

72 

1 

I  62 

2.4 
.57 

2.4 

57 

Ik.  4 
1*2 
*•  4 

•  2l  2 

FnprtiMi 

1 

I  75 

1; 

ji 

3.5 

Si 

163 

36 

• 

155 

36 

85 

152 

.43 

3.6 

81 

1 

153 

2.2 
.50 

3.1 

70 

OnirtiMtt 

1 

172 

26 

3.8 

1 

14 

3.9 

1 

2.1 

3.5 

Nl.  4 

Sena 

to  3 

'<zr 

;es 

28 

J9 

• 

IJI 

14 
33 

4.1 

H 

1 
1  49 

15 
33 

4.1 

90 

1 
149 

1.7 
J7 

4.1 

90 

1 
I  49 

2.0 
44 

2.8 
75 

3.' 

s: 

37 

2 

v« 

pmort.., 

Q«lllitl« 

t 

1.3 

2.3 

1 

1.7 

23 

1 

1.9 

2.3 

1 

2.2 
57 

2.2 

57 

1 
179 

% 

to 
1 

;9C 

1.3 

36 

26 
N 

!  ,'? 

1.7 
44 

26 

M 

1 

172 

1.9 

43 

2.5 

64 

1 
1.67 

2.2 

54 

2.4 

59 

1 
172 

2.7 

68 

I.T 

43 

OwoWiw 

8 

iv2 

r  Mri 

182 

1.3 

35 

3.0 

80 

i  es 

1.7 
43 

3  0 

75 

163 

1.9 

46 

3.0 
73 

1 
161 

2.1 

50 

29 

68 

1 

162 

2.6 
63 

2.2 

53 

OWM* 

8 

2 

PKfMliMU 

175 

1.3 

33 

1 

1.1 

3  4 

1 

1.8 

35 

1 

152 

2.0 

45 

3.4 

77 

1 

153 

2.4 

62 

2S 

66 

3 

2'/i 

Pl*f*rtiM> 

Oiwtite 

III 

33 

55 

1  56 

37 

v 

1 
151 

1.7 

37 

39 

87 

1 

149 

2.0 
44 

3.8 

84 

150 

2.2 
51 

3.3 

74 

H 
fe 

3 

Pntwten 

.  68 

1.2 

• 

38 

• 

1 

in 

1.6 

37 

39 
91 

1 

149 

1.7 
37 

4.0 

S3 

149 

1.9 
42 

4.0 

82 

1 

I  49 

2.: 

48 

3.5 

77 

M 

to 

v« 

Prttwti... 

1 
196 

1.5 
44 

2.3 

B 

1 

1  85 

1.9 

5: 

22 
.61 

1 

182 

2.1 
56 

2.2 
59 

175 

2.3 

59 

2.1 

54 

179 

25 

.75 

1.3 

.34 

9 

1 

Omttin 

190 

1.5 

25 

1 

1.9 

2.5 

1 
172 

2.1 
S3 

24 

ei 

If? 

23 

57 

24 

£9 

1 
1.72 

2.3 
7J 

1.6 
41 

by  that  formula  for  average  conditions.  A  relative  consistenc}' 
of  1.10  is  about  right  for  road  work;  of  1.25  for  reinforced  con- 
crete bridges  if  a  drier  mixture  cannot  be  used. 

A  Table  of  Proportions  issued  by  the  Portland  Cement 
Association  over  the  name  of  A.  N.  Johnson  will  simplify  the 
application  of  Abrams'  theory: 

The  accompanying  table  shows  the  various  proportions  by  which  to 
combine  a  variety  of  fine  aggregates,  five  selected  sizes,  with  various  sizes  of 
coarse  aggregates.  The  fine  aggregates,  or  sands,  shown  in  the  table 
include,  first,  one  with  all  particles  passing  a  sieve  with  28  openings  per 
linear  inch  and  another  with  14  openings,  one  with  8,  one  with  4  and  a 
sand  with  |-inch  size  particles  down.  The  range  of  coarse  aggregate  is 
apparent  from  the  table. 

To  determine  whether  a  given  aggregate  is  to  be  classed  as  3-inch  or 


TABLES    OF    PROPORTIONS 


257 


Abrams'  Table  of  Proportions  and   Quantities  for 
One  Cubic  Yard  of  Concrete 

Based  upon  laboratory  investigations,  using  approved  materials,  compres- 
sive  strength,  28  days,  with  workable  plasticity,  6  by  12-inch  cylinders,  S,<W0 
pounds  per  square  inch. 


SIZES 

FINE  AGGREGATES,  SCREEN  OPE 

INGS  PER  INCH 

I 

j||j 

0-28 

0-14 

0-8 

O-4 

0-%  In. 

I 

| 

j 

I 

1 

J 

1 

1 

I 

I 

1 

j 

j 

1 

1 

lo 

Qucntitic! 

182 

1.4 
.37 

2.8 

.75 

1 
1.68 

1.9 

.47 

2.9 

.73 

1 

1.63 

2.1 

.51 

2.9 

1 

1.61 

2.2 

.52 

2.8 

.66 

162 

2.7 

.65 

2.1 

.51 

to 
2 

175 

1.4 

36 

3.3 

.86 

1 
163 

1.9 

.46 

3.3 

.75 

1 

1.55 

2.0 

.46 

3.4 

.78 

1 

1.52 

2.2 

.50 

3.3 

.74 

1.53 

2.7 

.62 

2.7 

.62 

2^ 

lo2 

2'/z 

'/2 

to 
3 

3/4 

to 

J/4 
1'/2 

-                 . 

1 

1.72 

1.4 

35 

3.6 

.91 

1.58 

1.8 

.43 

3.6 

.85 

1 

1.51 

1.9 

.42 

3.7 

.83 

1 
1.49 

2.1 

.46 

3.7 

.81 

1 
1.50 

2.6 

.57 

3.1 

.69 

Outntrlie! 

1 

;158 

1.3 

33 

3.7 

.92 

1.58 

1.8 

.42 

3.8 

.89 

149 

1.8 

.40 

3.9 

.86 

1 

1.49 

2.1 

.46 

4.0 
.88 

1 

1.49 

2.4 

.53 

3.3 

.63 

OucMBe. 

'Z!1 

i.90 

48 

.68 

1.77 

.55 

2.4 

.63 

1 
172 

2.4 

.61 

2.1 

.53 

1 
1.67 

2.6 

.64 

2.2 

.55 

1 

1.  72 

3.1 

.79 

1.5 

.39 

CutitliBoi 

1 

1.32 

1.1 

46 

2.7 

.73 

1.79 

2.0 

.50 

2.8 

.70 

1 

1.63 

2.3 

.55 

2.7 

.65 

1 

1.61 

2.5 

.59 

2.7 

.64 

1 

1.62 

3.0 
.73 

2.0 

.48 

2 

oil. 

1 

1.75 

1.7 

.44 

3.1 

80 

1 

163 

2.0 

.48 

3.1 

.75 

1 

1.55 

2.3 

.53 

3.1 

.72 

1 

152 

2.5 

.56 

3.0 

.67 

1 

1.53 

3.0 

.68 

2.4 

.55 

J/4 

to 

~%~ 

lo 
3 

ProportioM 

Qu«MiS«i 

1 
1.72 

1.7 
.43 

3.3 

84 

163 

2.0 

.47 

2.0 

.47 

3.5 

.83 

1 

1.51 

2.3 

.52 

3.4 

1 

1.49 

2.4 

.53 

3.4 

.75 

1 

1.  50 

2.9 

64 

2.8 

.62- 

3.1 

.68 

Pn|»rtio»i 

QiKittitiei 

1 
168 

1.7 

.43 

3.5 

88 

158 

3.7 

.87 

149 

2.3 

51 

3.7 

81 

1 

1.49 

2.4 

.53 

3.6 

.79 

1 
1.49 

2.8 

62 

to 

Quntitie! 

1 

182 

1.7 

46 

2.8 
.75 

1 

168 

2.0 

.50 

2.9 

.73 

1 
163 

2.3 

.55 

2.7 

.65 

1 

1.61 

2.6 

62 

2.6 

.62 

1 

1.62 

3.1 

.75 

2.0 

.48 

1 
to 

2 

lo 

2'/2 

It 

3 

Proportions 

1 

175 

1.5 

.39 

3.2 

.83 

1 

163 

1.9 

.46 

3.5 

.85 

1.58 

2.2 

51 

3.3 

76 

1 
1.52 

2.4 

54 

3.3 

.74 

1 

1.53 

3.0 

.68 

2.6 

.59 

PropertWU 

1 
172 

1.4 

.35 

3.4 

86 

1 

1.58 

1.9 

.45 

3.8 

.89 

1 
1.51 

2.0 

.44 

3.7 

.83 

1 

1.  49 

2.3 

.51 

3.7 

.81 

1 
1.50 

2.7 

.59 

3.1 

.69 

Proportion! 

Ouintifc, 

1 

167 

1.3 
.33 

3.6 

90 

158 

1.8 

.42 

4.0 

.94 

1.49 

2.0 

44 

3.9 

86 

1 
1.49 

2.2 

.48 

3.9 

.86 

1 
1.49 

2-7 

.59 

3.3 

.73 

2^-inch  or  2-inch,  or  whatever  the  upper  limit  of  size  may  be  there  should 
be  not  less  than  10  per  cent  of  the  sample  between  the  upper  limit  and  the 
next  lower  size.  Thus,  if  a  material  is  to  be  classed  as  a  3-inch  aggregate 
there  should  be  not  less  than  10  per  cent  of  the  total  volume  of  the  sample 
between  the  3-inch  and  2^-inch  sizes;  otherwise  it  will  be  classed  as  2|-inch 
size.  Similarly,  if  there  are  2-inch  pieces  it  will  be  classed  as  2-inch  aggre- 
gate if  there  is  not  less  than  10  per  cent  between  1-2 -inch  and  2-inch  sizes. 

For  fine  aggregates  there  should  be  of  the  coarser  material  not  less  than 
15  per  cent  between  the  coarser  size  and  the  next  smaller  screen  opening. 
Thus,  if  a  fine  aggregate  is  to  be  classed  as  j-inch  size  there  should  be  not 
less  than  15  per  cent  between  the  |-inch  screen  and  the  J-inch  screen. 

With  the  i-irich  sand  down,  the  one  usually  specified,  and  with  the 
coarse  aggregate  varying  from  that  held  on  a  No.  4  sieve  to  that  passing  a 
1 1-inch  opening,  the  usual  proportions  of  1  :  2  :  3  were  taken  and,  with  a 
workable  plasticity  or  practical  consistency,  such  a  mixture  produces  a 


258 


CONCRETE   ROADS 


concrete  with  a  crushing  strength  at  twenty-eight  days  of  3000  pounds  pei 
square  inch  in  the  form  of  6  X  12-inch  cylinders.  All  of  the  other  propor- 
tions and  combinations  are  computed  to  give  the  same  strength  concrete  as 
1:2:3  mixture. 

TABLE  III 
QUANTITY  OF  MIXING  WATER  REQUIRED  FOR  CONCRETE 


Mix 

GALLONS  OF  WATER  PER  SACK  OF  CEMENT" 

Cem.- 

USING  AGGREGATES  OF  DIFFERENT  FINENESS  MODULI 

Agg. 

by 

Vol. 

1.50 

2.00 

2.50 

3.00 

3.50 

4.00 

4.50 

5.00 

5.50 

6.00 

6.50    7.00 

Relative  Consistency  -  (R)  =1.00 


1-12 

23.5 

21.4 

19.5 

17.8 

16.4 

15.2 

13.9 

12.9 

12.0 

11.1 

10.4 

9.8 

1-9 

18.1 

16.7 

15.2 

14.0 

12.9 

12.0 

11.0 

10.2 

9.6 

9.0 

8.4 

7.9 

1-7 

14.7 

13.5 

12.3 

11.4 

10.6 

9.9 

9.1 

8.6 

8.0 

7.6 

7.2 

6.7 

1-6 

13.0 

12.0 

11.0 

10.2 

9.5 

8.9 

8.3 

7.7 

7.3 

6.8 

6.5 

6.2 

1-5 

11.2 

10.4 

9.5 

8.9 

8.3 

7.8 

7.3 

6.9 

6.4 

6.1 

5.8 

5.5 

1-4 

9.5 

8.9 

8.2 

7.7 

7.2 

6.8 

6.3 

6.0 

5.7 

5.4 

5.2 

5.0 

1-3 

7.8 

7.2 

6.7 

6.3 

6.0 

5.7 

5.4 

5.1 

4.9 

4.6 

4.5 

4.3 

1-2 
1-1 

6.0 
4.3 

4.1 

3.9 

3.8 

3.7 

3.6 

3.5 

3.4 

3.3 

3.2 

3.9 
3.2 

3.8 
3.1 

Relative  Consistency  -  (R)  =1.10 


1-12 

25.8 

23.6 

21.4 

19.6 

18.1 

16.7 

15.3 

14.2 

13.2 

12.2 

11.4 

10.8 

1-9 

19.9 

18.4 

16.7 

15.4 

14.2 

13.2 

12.1 

11.2 

10.6 

9.9 

9.2 

8.7 

1-7 

16.2 

14.9 

13.5 

12.5 

11.7 

10.9 

10.0 

9.5 

8.8 

8.4 

7.9 

7.4 

1-6 

14.3 

13.2 

12.1 

11.2 

10.5 

9.8 

9.1 

8.5 

8.0 

7.5 

7.2 

6.8 

1-5 

12.3 

11.4 

10.5 

9.8 

9.1 

8.6 

8.0 

7.6 

7.0 

6.7 

6.4 

6.1 

1-4 

10.5 

9.8 

9.0 

8.5 

7.9 

7.5 

6.9 

6.6 

6.3 

5.9 

5.7 

5.5 

1-3 

8.6 

7.9 

7.4 

6.9 

6.6 

6.3 

5.9 

5.6 

5.4 

5.1 

5.0 

4.7 

1-2 

6.6 

6.3 

5.9 

5.6 

5.4 

5.2 

5.0 

4.7 

4.5 

4.4 

4.3 

4.2 

1-1 

4.7 

4.5 

4.3 

4.2 

4.1 

4.0 

3.9 

3.7 

3.6 

3.5 

3.5 

3.4 

Relative  Consistency  —  (R)  =1.25 


1-12 

29.4 

26.8 

24.4 

22.2 

20.5 

19.0 

17.4 

16.1 

15.0 

13.9 

13.0 

12.3 

1-3 

22.6 

20.9 

19.0 

17.5 

16.1 

15.0 

13.8 

12.7 

12.0 

11.2 

10.5 

9.9 

1-7 

18.4 

16.9 

15.4 

14.3 

13.2 

12.4 

11.4 

10.7 

10.0 

9.5 

9.0 

8.4 

1-6 

16.3 

15.0 

13.8 

12.8 

11.9 

11.1 

10.4 

9.6 

9.1 

8.5 

8.1 

7.7 

1-5 

14.0 

13.0 

11.9 

11.1 

10.4 

9.8 

9.1 

8.6 

8.0 

7.6 

7.2 

6.9 

1-4 

11.9 

11.1 

10.2 

9.6 

9.0 

8.5 

7.9 

7.5 

7.1 

6.8 

6.5 

6.2 

1-3 

9.8 

9.0 

8.4 

7.9 

7.5 

7.1 

6.8 

6.4 

6.1 

5.8 

5.6 

5.4 

1-2 

7.5 

7.1 

6.8 

6.4 

6.1 

5.9 

5.6 

5.4 

5.1 

5.0 

4.9 

4.8 

1-1 

5.4 

5.1 

4.9 

4.8 

4.6 

4.5 

4.4 

4.3 

4.1 

4.0 

4.0 

3.9 

TABLES  OF  PROPORTIONS  259 

The  table  contains  in  the  upper  line  of  each  block  the  proportion  of 
cement,  fine  and  coarse  aggregate  to  be  combined,  while  immediately 
below  in  each  square  are  given  the  quantities  that  are  required  for  a  cubic 
yard  of  concrete,  the  cement  quantity  being  given  in  barrels  and  hun- 
dredths  of  barrels  and  the  quantities  for  fine  and  coarse  aggregates  being 
given  in  hundredths  of  cubic  yards. 

It  should  be  borne  in  mind  that  the  quantities  shown  in  the  table  are  for 
a  cubic  yard  of  concrete  as  determined  from  laboratory  measurements  and 
that  for  the  purpose  of  ordering  materials  or  making  estimates  of  the  total 
cost  of  materials  for  a  given  piece  of  work  these  quantities  should  be 
increased  from  the  amounts  shown  by  such  estimate  of  waste  for  the  aggre- 
gates as  experience  in  handling  the  work,  according  to  the  particular 
method  to  be  employed,  has  indicated  as  necessary. 

The  following  example  will  make  clear  the  use  of  the  table : 

It  will  be  supposed  that  one  sand  is  that  usually  specified,  from  j-inch 
down,  and  must  be  shipped  in  at  a  cost  of  $2  per  cubic  yard  and  that  one 
coarse  aggregate,  varying  from  j-inch  to  2  inches,  must  also  be  shipped  in 
at  a  total  cost  of  $3  per  cubic  yard;  that  there  is  available  locally  a  supply 
of  sand  and  coarse  aggregate,  each  being  rather  fine,  the  sand  varying  from 
f-inch  down  which  costs  $1.50  per  cubic  yard,  while  the  coarse  aggregate 
varies  from  j-inch  to  1  inch  and  may  be  secured  at  a  cost  of  $2.50  per  cubic 
yard.  The  cement  in  each  case  is  assumed  to  cost  $3  per  barrel.  The 
cost  of  a  cubic  yard  of  concrete  using  the  materials  to  be  shipped  in  would 
then  be  as  follows: 

1.52  barrels  cement at  $3.00  =  14.56 

.43  cubic  yard  of  sand at  $2.00=      .86 

.81  cubic  yard  of  coarse  aggregate at  $3.00=  2.43 

Total  cost  of  materials  for  1  cubic  yard  concrete  $7 . 85 

Using  local  materials  the  cost  would  be: 

1.72  barrels  cement at  $3.00  =  $5. 16 

.  46  cubic  yard  of  sand at  $1 . 50  =      .69 

.  66  cubic  yard  of  coarse  aggregate at  $2 . 50  =   1 . 65 

Total  cost  of  materials  for  1  cubic  yard  concrete .' $7 . 50 

Thus  the  local  aggregate,  in  this  instance,  although  fine  and  requiring 
more  cement,  will  produce  a  yard  of  concrete  at  less  cost.  In  general  it 
will  be  found  that  the  use  of  finer  sand  or  finer  aggregate  increases  the 
amount  of  cement,  the  opposite  being  true  for  coarser  sizes.  Thus  a 
coarse  aggregate  with  all  of  the  fine  material  removed,  varying  from  1  inch 
to  3  inches  in  size,  combined  with  sand  varying  from  J  inch  down,  uses 
1.49  barrels  of  cement;  whereas  an  aggregate  varying  from  1  inch  to  j  inch 


260  CONCRETE   ROADS 

combined  with  the  same  sand,  \  inch  down,  requires  1.67  barrels  of  cement 
for  a  cubic  yard  of  concrete. 

If  the  producer  of  aggregate  materials  can  say  what  are  the  sizes  of 
aggregates  he  can  furnish  they  can  be  used  to  make  a  concrete  of  a  given 
strength.  Should  concrete  of  a  strength  other  than  3000  pounds  per 
square  inch  be  desired,  then  another  table  would  be  calculated  with  the 
proportions  and  quantities  required  accordingly,  but  the  table  given  here  is 
confined  to  the  use  of  concrete  for  concrete  roads  where  a  better  quality  and 
greater  strength  are  required  than  is  necessary  for  concrete  for  many  other 
structures. 

Edwards*  Surface  Area  Method. — L.  N.  Edwards  proposed 
a  method  l  of  proportioning  concrete,  in  1918,  on  the  theory 
that  "  The  strength  of  mortars  is  dependent  upon  (1)  the 
quantity  of  cement  in  relation  to  the  surface  areas  of  the  aggre- 
gates, and  (2)  the  consistency  of  the  mix;  that  the  strength  of 
mortars  of  uniform  consistency  containing  sand  aggregates  of 
varying  granulometric  composition  is  directly  proportional 
to  the  quantity  of  cement  they  contain  in  relation  to  the  sur- 
face area  of  the  aggregate." 

Mr.  R.  B.  Young2  has  determined  a  series  of  diagrams 
for  getting  the  relation  of  the  surface  area  and  the  grading. 
From  these  diagrams  Mr.  Edwards'  method  may  be  applied 
without  extended  computations. 

Some  Proportions    Used  in  Practice 

A  concrete  pavement  laid  at  Bellefontaine,  Ohio,  in  1893,  had  a  4-inch 
base  of  one  part  Portland  cement  to  four  parts  gravel.  The  top  course 
2  inches  thick  was  one  Portland  cement  to  one  of  clean  sand. 

Richmond,  Ind.,  in  1903  laid  a  5-inch  base  of  1  :  2  :  5  mixture  and 
11-inch  wearing  surface  of  either  1  part  cement  to  1  part  coarse  sand  or  1 
part  cement  to  1  part  sand  to  1  part  stone  screenings. 

Lemars,  Iowa,  1904,  5-inch  base  1  :  6  gravel;  l|-inch  wearing  surface 
1  :  2  sand. 

Independence,  Mo.,  crushed  stone  and  sand  mixed  in  the  proportion 
of  1  :  7  for  SHnch  base  and  2  :  3  for  If-inch  top. 

Mason  City,  la.,  1:2:5  mixture  for  5-inch  base  and  1  :  2  for  2-inch 
wearing  surface. 

1  Proceedings,  American  Society  for   Testing  Materials,  Vol.  XVIII, 
Part  II. 

2  Engineering  News-Record,  Vol.  LXXXIV,  Jan.,  1920. 


QUANTITY  FORMULAS  261 

Sioux  City,  la.,  one  course  5  inches  thick.  Mixed  to  overfill  voids 
5  per  cent.  If  voids  were  not  determined  a  1  :  3  :  4|  was  used. 

Wayne  County,  Mich.  Roads  constructed  in  1911  consist  of  the  single 
course  type;  the  concrete  being  1:1^:3,  depth  7  inches. 

Scotia-High  Mills  road,  Schenectady,  N.  Y.,  1  :  1£  :  3.  (1914).  Other 
New  York  road  same  proportions. 

Tupelo-Saltillo,  Lee  county,  Miss.,  1:2:3.     (1914.) 

Macon,  Ga.,  1913,  1:2:3.     5  to  7  inches  thick. 

Pennsylvania  Highway  Commission,  1916.     1:2:3. 

Dupont  Road,  Delaware.  This  is  a  very  carefully  constructed  road. 
A  testing  laboratory  was  maintained  on  the  work  and  constant  tests  made 
of  all  materials.  The  proportion  was  changed  frequently  to  conform  to  the 
materials  used. 

Proportioning  the  Very  Fine  Aggregate. — Not  much  atten- 
tion has  been  paid  to  this  part  of  the  concrete.  On  the  other 
hand,  with  asphalt  pavements  very  great  attention  is  given  to 
the  fine  sand  and  stone  dust  used  even  to  the  portion  which 
passes  a  No.  200  sieve.  Sufficient  tests. and  studies  have  been 
made,  however,  to  prove  that  the  addition  of  fine  material,  such 
as  clay  or  hydrated  lime,  will  improve  lean  concretes.  This 
fine  material  not  only  fills  the  voids  and  makes  the  mortar 
denser  but  improves  its  plasticity.  Hydrated  lime,  no  doubt, 
adds  some  cementing  properties  and  is  therefore  better  than 
stone  dust  or  clay.  But  tests  of  strength  and  density  and  the 
increased  cost  must  be  the  determining  factors  for  its  use. 

Quantities  of  Materials. — Fuller's  rule  for  quantities  is  as 
follows: 1 

Divide  11  by  the  sum  of  the  parts  of  all  the  ingredients, 
and  the  quotient  will  be  the  number  of  barrels  of  Portland  cement 
required  for  1  cubic  yard  of  concrete.2 

To  express  this  rule  algebraically 

Let  c  =  number  of  parts  cement ; 

s  =  number  of  parts  sand ; 
g  =  number  of  parts  coarse  aggregate. 

1  Taylor  and  Thompson's   "  Concrete,  Plain  and  Reinforced,"  p.  16, 
Wiley  &  Sons,  New  York. 

2  The  constant  10.3  is  also  used;  see  Mills'  "  Materials  of  Construction," 
p.  177.     John  Wiley  &  Sons,  N.  Y. 


262  CONCRETE  ROADS 

Then  -        —  =  P  =  number  of  barrels  Portland  cement  required 
c+s+g 

for  1  cubic  yard  concrete. 

Since  a  barrel  of  cement  is  now  reckoned  as  4  bags  and  a  bag  of 
cement  weighing  94  pounds  as  1  cubic  foot,  there  results  : 
With  the  proportions 

cement  :  sand  :  gravel  or  stone  =  c  :  s  :  g, 
1  cubic  yard  of  concrete  will  require 

Cement,  barrels,  =  P  =  —  ;  ---- 
c+s+g 

Sand  (cu.  yd.)  =  PXsX4/27 

Coarse  aggregate  (cu.  yd.)  =PX<?X4/27 

PROBLEM  :  A  roadway  is  to  be  paved  18  feet  wide,  6  inches  thick  for  a 
distance  of  \  mile.    Required,  the  quantities  for  a  1  :  2  :  3  concrete. 
SOLUTION:  Total  number  of  yards  of  concrete  required 

||1  -TxS5xiofl78° 

=  440  cubic  yards 

P 

= 


Cement  =  —  X440  =  805  barrels 


Sand      =      X2x 

O  -i 

=  239  cubic  yards 

Coarse  aggregate  =^X3X^X440 
=  359  cubic  yards. 

If  the  coarse  aggregate  is  screened  to  a  uniform  size,  about  5  per  cent 
should  be  added;  if  graded  from  coarse  to  fine,  so  as  to  be  quite  dense, 
deduct  5  per  cent. 

Taylor  and  Thompson's  Ride.  —  Taylor  and  Thompson  l  have  worked 
out  quite  a  complete  formula  which  they  have  simplified  to  the  following 
working  formula  for  average  materials: 

B_  _  27  _ 

2.  61  +0.7235  +  1.  08(1  -v)G> 

1  "Reinforced  Concrete,"  p.  224. 


QUANTITY  FORMULAS 


263 


where  B=  number  of  barrels  cement  per  cubic  yard  of  concrete; 
S  =  volume  of  loose  sand  in  cubic  feet; 
v  =  absolute  voids  1  in  stone  determined  by  weight  method; 
G  =  volume  of  broken  stone  or  gravel  or  cinders  in  cubic  feet. 

Now  if  c,  s,  and  g  represent  the  proportional  parts  of  cement,  sand  and 
stone  in  the  mixture,  as  before, 

Cement  in  barrels  =  B 
Sand  in  cubic  yards =#XsX4/27 
Stone  in  cubic  yards  =  5X0X4/27 

Applying  this  formula  to  the  same  problem  with  average  limestone  rock 
having  absolute  voids  of  40  per  cent : 

The  proportions  are  1:2:3; 

1  The  method  of  finding  the  voida  is  made  as  follows: 

Pour  into  a  16-quart  pail  31  pounds  2  ounces  of  water  and  mark  the  level  of  the 
surface.  The  pail  up  to  this  mark  contains  5  cubic  foot  of  any  material. 

Weigh  the  empty  pail. 

Fill  the  pail  to  the  required  level  with  the  material. 

Weigh  and  deduct  the  weight  of  the  empty  pail.  Call  the  net  weight  of  a  cubic  foot 
of  the  material  S. 

Dry  a  sample — about  10  pounds — of  the  material  at  a  temperature  of  boiling  water, 
212°  F.,  until  there  is  no  further  loss.  Calculate  the  loss  in  weight  or  moisture  in  per- 
centage of  the  original  moist  weight.  Express  this  as  p. 

R  =  weight  of  solid  rock  per  cubic  foot  =  weight  of  a  cubic  foot  of  water  multiplied  by 
the  specific  gravity  of  the  rock  =62.46  Xspecific  gravity  of  the  rock. 


Then 


100 


AVERAGE  SPECIFIC   GRAVITY   OF   VARIOUS  AGGREGATES 


Material 

Specific  Gravity 

Weight  of  Solid 
Cubic  Foot  of 
Rock, 
Ib. 

Sand                       .            

2.65 

165 

Gravel                  

2.66 

165 

Conglomerate     

2.6 

162 

Granite                      

2.7 

168 

Limestone                                     

2.6 

162 

Trap                        *              

2.9 

180 

Slate                                         

2.7 

168 

Sandstone                               .      

2.4 

150 

1  5 

95 

264  CONCRETE   ROADS 

therefore  if  cement  be  taken  as  1  barrel 

S  =  2  barrels  =  8  cubic  feet,  and  G  =  12  cubic  feet 
27 


B  = 


2.61+0.724X8  +  1.08  (1-.40)  12 
27  27 


2.61+5.784+7.776     16.17 
=  1.67 
Then  for  the  whole  job  will  be  required 

Cement  (barrels)  440  X 1 .67  =  735 

Sand  (cubic  yards)  735X2X4/27     =218 
Stone  (cubic  yards)  735  X  3  X  4/27    =  32 

PROBLEM. — If  Mills'  rule  were  used,  what  would  be  the  quantities? 
If  Abrams'  Table? 


FIG.  136.— Tilting  Drum  Mixers. 

The  Specification  of  the  Concrete  Institute,  that  a  cubic 
yard  of  concrete  in  place  shall  contain  not  less  than  1.7  barrels  of 
cement  falls  between  Fuller's  rule  (1.83)  and  Taylor  and 
Thompson's  rule  (1.67),  and  agrees  with  Mills'  rule  (1.71), 
but  all  are  greater  than  the  quantity  given  in  Abrams'  Table 
(1.61). 

Mixing  the  Concrete. — The  method  of  hand  mixing  was 
explained  in  Chapter  X,  p.  207.  Machine  mixing  only  will  be 
considered  here. 

Mixers. — A  number  of  different  mixers  have  been  placed 
upon  the  market  and  these  have  been  generally  classified  as 
"  batch  mixers "  and  "  continuous  mixers."  In  the  batch 


MIXERS  265 

mixer  measured  quantities  of  the  several  ingredients  are  placed 
in  the  mixer,  these  mixed  together  and  removed;  then  a  second 
charge  or  batch  is  mixed  and  removed;  and  so  on  indefinitely. 
In  the  continuous  mixer  the  materials  are  fed  into  the  machine 
in  a  continuous  stream  in  presumably  right  proportions  at  one 
place  and  the  mixed  concrete  is  continuously  discharged  at 
another.  The  difficulty  of  thorough  control  of  the  feeding  due 
to  choking  valves,  pipes,  irregularities  of  the  materials  or  laziness 
of  workmen  have  brought  engineers  and  contractors  to  favor 


FIG.  137. — Showing  interior  of  Drum,  and  Loading  Skip. 

generally  the  batch  mixer.  If  the  feeding  could  be  made  auto- 
matic and  absolutely  regular  there  would  be  some  advantages  in 
the  continuous  mixer  With  the  batch  mixer  the  quantities  are 
measured  out  beforehand  and  all  put  in  the  mixer  at  once. 
The  homogeneity  of  the  product  depends  on  the  character  and 
time  of  mixing,  which  is  easily  regulated. 

Mixers  are  further  classified  as  Rotary,  Paddle,  and  Gravity. 
A  rotary  mixer  is  essentially  a  chamber,  drum,  box  or  barrel 
into  which  the  materials  to  be  mixed  are  introduced.  The 


266 


CONCRETE  ROADS 


chamber  is  rotated  on  trunnions  and  the  tumbling  of  the 
materials  thoroughly  mixes  them  together.  All  of  the  modern 
mixers,  except  those  used  for  dry  mixing,  are  open  at  the  ends 
of  the  drum  to  facilitate  examination  of  the  mixing  concrete 
and  that  they  may  be  charged  and  discharged  without  stopping. 
Blades  or  cleats  on  the  inside  of  the  chamber,  Figs  136  and  137, 
carry  the  materials  up  the  side  and  as  they  pour  off  the  blades 
and  drop  to  the  bottom  of  the  drum,  they  are  deflected,  cut  and 
kneaded  in  such  a  way  that  a  very  thorough  mixing,  com- 


FIG.  138.— Paddle  Mixer. 

mingling  and  coating  is  accomplished.  The  larger  machines 
have  loading  skips,  Fig.  137,  so  arranged  that  the  materials 
may  be  dumped  into  the  skip  while  a  batch  is  being  mixed; 
as  soon  as  the  mixing  chamber  is  discharged  the  loaded  skip  is 
mechanically  emptied  into  it.  The  loading  of  the  skip  and 
the  mixing  going  on  together  makes  the  loss  of  time  due  to 
charging  and  discharging  a  minimum. 

Paddle  Mixers. — Fig.  138  shows  a  paddle  mixer.     It  con- 
sists of  an  open  box  in  which  revolve  in  opposite  direction  two 


MEASURING   MATERIALS  267 

shafts  having  attached  to  them  the  paddles.  It  is  placed  on  a 
platform  and  the  materials  introduced  at  the  top  by  shovels, 
barrows  or  otherwise.  The  mixed  concrete  is  discharged  through 
an  opening  in  the  bottom  through  the  platform  into  barrows, 
wagons,  carts  or  other  conveyors.  It  may  be  used  either  as  a 
batch  or  continous  mixer  by  proper  arrangement  of  the  pad- 
dles and  exit  valve.  Other  paddle  mixers  have  but  a  single 
shaft  with  the  paddles  arranged  in  a  spiral  along  it  so  that  the 
materials  entering  at  one  end  are  pushed  along  and  mixed  and 
then  finally  discharged  at  the  other  end.  Such  a  mixer  is  of 
the  continuous  type.  Fig.  139  shows  a  portable  concrete  mixer 
of  the  paddle  type. 

Gravity  Mixers.^Gravity  mixers    require    no    power  to 


FIG.  139.— Paddle  Type  Mixer,  Portable. 

operate  them,  the  mixing  being  done  by  dropping  the  material 
down  a  vertical  trough  or  chute,  Fig.  140,  in  which  are  obstruc- 
tions or  baffles.  These  baffles  throw  the  material  from  side 
to  side  of  the  chute  mixing  it  as  it  falls.  Water  is  introduced 
through  convenient  pipes.  Iron  gratings  serve  to  cut  up  any 
cement  balls  that  might  form.  Other  forms  of  gravity  mixers 
have  been  designed,  but  as  this  type  of  mixer  is  little  used  for 
road  work  they  will  not  be  described. 

Measuring  the  Materials. — The  94-lb.  bag  of  cement  is 
ordinarily  considered  to  be  one  cubic  foot.  With  sand  and 
stone  loose  measurements  are  usually  assumed.  A  measuring 
box  was  described  in  Chapter  X,  page  207,  which  can  be  used 


268 


CONCRETE   ROADS 


for  measuring  or  checking  as  desired.  Wheelbarrows,  Fig.  141, 
are  now  so  made  that  they  may  be  struck  off  smooth  on 'top 
and  contain  exactly  three,  or  four,  cubic  feet.  With  such 
barrows  the  quantities  can  be  measured  with  reasonable  accu- 
racy. 

Automatic  Measuring  Devices  have  not  proven  entirely 
satisfactory  owing  to  their  liability  to  become  clogged  or  choked. 
One  of  them  consists  of  a  series  of  cylinders  in  vertical  positions 
with     their    open     bottoms 
above  and  slightly  separated 
from  revolving  disks.     As  the 
disks    revolve  the    materials 
in  them  flow  out  on  to  the 
disks  in  cone-shaped  masses. 
An  adjustable    blade   is  ar- 
ranged to  peel  off  from  the 
cone     a     definite    amount. 


\      Hopper       / 


Discharge  Pipe 

FIG.  140. 


FIG.  141. — Measuring  Barrows. 


Other  devices  have  a  roll,  and  others  a  moving  belt  to  drag 
out  from  an  adjustable  opening  at  the  lower  end  of  a  hopper 
the  material. 

Weighing  Devices. — It  is  entirely  feasible  to  proportion 
by  weight.  This  has  been  done  for  years  in  the  construction  of 
bituminous  pavements.  The  stone  and  sand  are  elevated  from 


CONSISTENCY  OF  CONCRETE  269 

the  screen  to  bins  above  a  hopper  which  rests  on  a  scale  having  a 
number  of  weighing  beams.  A  poise  is  moved  out  on  one  of 
the  beams  until  it  comes  to  a  stop  clamped  at  a  place  to  indicate 
the  amount  of  one  of  the  ingredients  of  the  mixture.  The 
valve  in  a  bin  spout  is  opened,  the  material  flows  until  the 
beam  raises,  the  valve  is  closed.  Another  poise  is  run  out  to 
its  stop,  another  bin  is  opened,  and  so  on  until  all  the  ingre- 
dients and  grades  are  in  the  hopper.  The  valve  in  the  bottom 
of  the  hopper  is  now  opened  and  the  whole  charge  in  exact 
proportions  is  dropped  into  the  mixer.  Improvements  have  been 
made  on  these  scales  so  that  now  the  stops  may  be  placed  at 
the  proper  places  and  the  beam  locked  up;  a  pointer  only 
shows  on  the  outside.  A  man  in  authority  has  the  key;  no 
one  else  can  change  the  proportions. 

Consistency. — The  United  States  Bureau  of  Standards  has 
six  different  consistencies  for  concrete  as  follows: 

Dry. — Containing  just  sufficient  water  to  cause  the  cement  and  sand  to 
adhere  after  tamping  and  removal  of  the  molds. 

Moist. — A  mean  between  the  dry  and  plastic  consistencies. 

Plastic. — Containing  the  maximum  of  water  which  allows  the  removal 
of  forms  immediately  after  molding.  The  surface  of  the  mass  shows  web- 
like  marks  of  neat  cement  and  water. 

Quaking. — A  stiff  mixture  upon  which  water  can  be  brought  to  the 
surface  by  light  tamping.  The  mass  should  not  flow  readily. 

Mushy. — A  soft  mushy  mixture  which  is  not  watery,  but  can  be  spaded 
and  readily  worked  into  place  to  the  form. 

Fluid. — A  watery  mixture  which  flows  readily  into  place  in  the  form 
with  little  or  no  mixing. 

Fig.  142  shows  three  batches  to  illustrate  the  consistencies 
"  quaking,"  "  mushy,"  and  "  fluid."  In  forming  the  piles 
the  concrete  was  allowed  to  slide  from  the  shovel  and  drop  only  a 
few  inches.  "  Quaking  "  to  "  mushy  "  would  be  the  proper 
consistency  for  road  work.  The  specification  of  the  Associa- 
tion of  American  Portland  Cement  Manufacturers  is,  "  The 
materials  shall  be  mixed  with  sufficient  water  to  produce  a 
concrete  which  when  deposited  will  settle  to  a  flattened  mass, 
but  shall  not  be  so  wet  as  to  cause  a  separation  of  the  mortar 
from  the  coarse  aggregate  in  handling." 


270 


CONCRETE  ROADS 


Slump  Test  for  Consist- 
ency.— This  consists  in  with- 
drawing the  mold  from  a 
cylinder  or  a  truncated  cone  of 
concrete  immediately  after 
casting  and  noting  the 
amount  it  decreases  in  height 
— slumps. 

Cylinder  Slump. — Professor 
Abrams  in  his  work  used  a 
6  X  12-inch  cylindrical  form, 
one  of  the  regular  molds  for 
casting  test  pieces,  made  of 
steel  gas  pipe  sawed  longi- 
tudinally along  one  side.  A 
clamp  holds  the  edges  of  the 
saw  kerf  tightly  together  while 
the  form  is  being  filled.  As 
soon  as  the  freshly  made  con- 
crete is  mixed  it  is  packed  into 
the  form,  the  clamp  loosened 
and  the  form  removed  by  a 
steady  upward  pull.  For  a 
relative  consistency  of  1.00 
(normal  consistency,  or  con- 
sistency for  maximum 
strength)  there  should  be  a 
slump  of  i  to  1  inch.  A  rela- 
tive consistency  of  1.10  gives 
a  slump  of  5  to  6  inches;  of 
1.25,  8  to  9  inches. 

Truncated  Cone  Slump. — 
Mr.  F.  L.  Roman,  Testing 
Engineer,  Illinois  State  High- 
way Department,  suggests  that 
a  truncated  cone  is  better  than 
a  cylinder  for  making  the 


SLUMP  TESTS 


271 


slump  tests.1  The  form  recommended  is  shown  in  Fig.  143.  It 
is  made  of  24-gauge  galvanized  iron  and,  manufactured  locally, 
costs  about  $2.50  each.  For  convenience  the  molds  are  pro- 
vided with  handles  and  foot  holds  of  strap  iron.  The  top  and 
bottom  is  turned  on  f -inch  wire  and  care  is  taken  that  the  cone 
is  circular  and  smooth  throughout. 
Mr.  Roman's  statement  is: 

When  making  a  slump  test  the  base  of 
the  truncated  cone  mold  is  placed  on  a 
flat  horizontal  surface,  and  filled  with  the 
concrete,  care  being  taken  to  tamp  or 
rather  arrange  the  mixture  in  the  appa- 
ratus to  obtain  dense  concrete  and  avoid 
stone  pockets,  as  large  voids  or  stone 
pockets  tend  to  cause  the  concrete  speci- 
men to  slump  on  one  side  rather  than 
vertically.  The  mold  is  removed  as  nearly 
vertically  as  possible  and  the  "  slump" 
or  vertical  settlement  (height  of  molded 
specimen  minus  height  of  concrete  after 
settlement)  is  determined.  Usually  the 
concrete  settles  and  comes  to  rest  almost 
as  quickly  as  the  mold  is  removed,  but  it 


FIG.  143.— Truncated  Cone 
Mold. 


is  advisable  to  take  all  readings  about  one  minute  after  the  mold  is 
removed. 

Experience  in  determining  the  consistency  of  concrete  with  the  trun- 
cated cone  apparatus  would  indicate  the  following  "slumps";  very  dry 
consistency,  no  "slump";  fairly  dry  consistency,  \  to  1  inch;  medium  to 
wet  consistencies,  1  to  4  inches;  wet  to  sloppy  consistencies,  4  to  8  inches; 
very  sloppy  consistencies,  above  8  inches.  It  should  be  noted,  however, 
that  crushed  stone  concrete  will  show  somewhat  less  slump  than  gravel 
concrete  of  the  same  consistency  due  to  the  fact  that  angular  fragments 
will,  to  some  extent,  be  held  in  place  mechanically  and  will  not  rearrange 
themselves  as  readily  as  the  round  pebbles.  The  difference  in  slump  due 
to  different  aggregates  is  at  least  apparent  at  the  drier  consistencies,  and 
for  future  state  highway  work  in  Illinois  one  general  requirement  only  is 
made,  that  all  concrete  for  pavements  shall  have  a  slump  of  \  to  1  inch. 

The  quantity  of  water  necessary  to  bring  the  concrete  to 
the  proper  consistency  depends  on  the  temperature  and  humid- 

1  See  "An  Apparatus  for  Determining  the  Consistency  of  Concrete," 
by  F.  L.  Roman,  in  Engineering  and  Contracting,  March  3,  1920. 


272 


CONCRETE   ROADS 


ity  of  the  atmosphere  and  the  character  and  condition  as 
regards  moisture  of  the  materials.  It  must  be  determined  each 
day,  and  thoughout  the  day,  by  those  in  charge. 

Laboratory  experiments  show  that  a  dry  mixture,  well- 
tamped,  makes  the  strongest  concrete.  But  as  tamping  is  hard 
work  and  the  probability  that  it  will  not  be  done  well  is  always 
present,  concrete  men  usually  prefer  a  wetter  mixture  as  more 
likely  to  be  homogeneous.  It  is  also  slightly  cheaper  as  the 
services  of  the  tampers  are  eliminated.  Professor  Duff  A. 
Abrams,  Professor  in  Charge,  Structural  Materials  Research 
Laboratory,  Lewis'  Institute,  Chicago,  says: 

The  only  safe  rule  to  follow  with  reference  to  water  in  concrete  is  to  use 
the  smallest  quantity  of  mixing  water  which  will  give  a  plastic  or  workable 
mix,  then  provide  plenty  of  moisture  for  the  concrete  during  the  period  of 
curing  which  follows  setting  and  hardening  of  the  cement. l 

Duration  and  Speed  of  Mixing. — Where  the  materials  are 
mixed  in  a  batch  mixer  the  mixing  should  continue  until  all 
the  particles  of  aggregate  are  completely  coated  and  the  con- 
crete of  proper  consistency.  Forty-five  seconds  after  the 
materials  are  in  the  drum  is  considered  enough.  The  recom- 
mended speed  at  which  the  drum  should  revolve  is  given  in  the 
following  table:2 


Rated  Capacity 

Capacity  Bags  of 

REVOLUTIONS  PER  MINUTE  OF  DRUM 

Cubic  Feet  Un- 
mixed Material 

Cement  in 
1:2:3  Mixtures 

Minimum 

Maximum 

7  to  11 

1 

15 

21 

12  to  16 

2 

12 

20 

18  to  23 

3 

12 

20 

24  to  29 

4 

11 

17 

30  to  33 

5 

10 

15 

1  See  Abram's  table,  p.  255. 

2  Extracted   from    "Report   of    Committee   on    Mixing    ard    Placing 
Materials,"  National  Congress  on  Concrete  Road  Building,  1914,  Chicago. 


STRIKE   BOARDS 


273 


Round  Rod 


5x3>*x  H  Angle 


PLAN 
-L  =  Width  of  Road +  20- 


f  ~     >JL_  V 

96 

ELEVATION 

TYPICAL   DESIGN    FOR  STRIKE   BOARD 


2  xK   Steel  Face 


<-G^      ^-  Eye  Bolt  for  Draw  Rods         •    >• 

* 17-0 — 


WOODEN   STRIKE  BOARD 


sr 

fj 

r'",n~f'g 
H-*  *i  t 


STEEL  TAMPER 


.-H 


and  Hole 


LONG  WOODEN   FLOAT 


x3x2     Wooden  Blocks 


-*  Round  Rods 


ELEVATION 
TYPICAL  DESIGN  FOR  FJNISHER'S   BRIDGE 

FIG.  144.— Typical  Designs  for  Strike  Boards,  Bridge  Float  and  Tamper. 
From  Bui.  249,  U.  S.  Dept.  of  Agriculture. 


274  CONCRETE  ROADS 

Retempering  mortar  or  concrete  is  not  allowable  and  all 
materials  should  be  emptied  from  the  drum  before  mixing  the 
next  batch. 

Placing  the  Concrete. — Before  placing,  the  subgrade,  which 
has  been  carefully  prepared  in  advance,  drainage  looked  after, 
rolled  and  compacted,  should  be  brought  to  an  even  surface. 
It  should  be  damp  but  not  muddy.  Concrete  laid  on  a  muddy 
surface  may  take  up  enough  muddy  water,  alkali  water  or  acid 
water  to  refuse  to  set  up  and  harden  normally. 

The  concrete  should  be  deposited  upon  the  subgrade  as 


FIG.  145. — Baker  Concrete  Road  Finisher. 

soon  as  possible  after  mixing.  Successive  batches  being  near 
enough  together  so  that  they  will  join  into  one  monolithic  mass. 
Otherwise  there  will  be  weak  places  which  may  afterward  induce 
cracks.  The  whole  width  of  the  roadway  should  be  deposited  to 
the  required  depth  in  a  continuous  operation.  Should  the 
machine  break  down  it  is  recommended  that  hand-mixed  con- 
crete be  used  to  complete  the  section  to  the  next  joint. 

Striking  Off,  Templates. — The  surface  of  the  concrete 
should  be  struck  off  with  a  template  or  strike  board.  This  may 
be  a  single  plank  curved  on  the  bottom  to  allow  for  the  crown  or 
it  may  be  of  much  more  elaborate  construction,  Fig.  144.  If  a 


FINISHING  275 

single  strike  board,  it  will  be  moved  forward  with  a  combined 
forward  and  transverse  motion.  When  within  3  feet  of  the 
transverse  joint,  the  board  is  lifted  to  the  joint  and  the  roadway 
struck  by  moving  the  board  away  from  the  joint.  Tem- 
plates may  be  made  of  two  planks  fastened  parallel  to  each 
other  about  2  feet  apart  and  drawn  along  the  roadway.  Extra 
concrete  is  kept  in  the  space  between  the  planks  which,  flowing 
under  the  second  plank,  fills  any  low  places  left  by  the  first. 

Much  more  elaborate  templates  are  being  made  up  of  steel 
I-beams  or  channels  bent  to  the  proper  cross-section  curve  and 
held  at  a  uniform  distance  apart  by  steel  spreaders.  They  rest 
on  rollers  or  carriages  at  the  end  with  finished  bearings  packed 
in  hard  oil.  They  are  drawn  forward  by  a  block  and  tackle  or 
by  a  cable  wrapped  about  a  drum  operated  by  the  mixer  engine. 
Fig.  145  shows  such  a  template. 

A  Joining  Straightedge  with  a  IJ-inch  slot  cut  upward  3 
inches  at  its  middle  point  is  recommended  by  the  State  High- 
way Commission  of  Wisconsin  to  prevent  the  slabs  on  opposite 
sides  of  the  joint  being  out  of  alignment.  The  straightedge 
is  constructed  from  a  Ijx 8-inch  plank,  6  feet  long;  the  edge  is 
beveled  and  shod  with  sheet  metal. 

Forms. — The  forms  along  the  outside  of  the  roadway  are 
placed  exactly  at  grade  and  on  them  the  strike  board  is  drawn. 
These  forms  may  be  wooden  plank  against  stakes  or  they  may  be 
steel  angles,  channels  or  rails. 

Finishing. — After  being  brought  to  the  proper  grade  by  the 
strike  board  the  surface  is  usually 
finished  with  wooden  floats  from 
the  bridge.  The  bridge  is  arranged 
so  that  no  part  of  it  touches  the 
concrete  surface.  The  finished 
surface  should  be  true  to  shape, 
not  varying  more  than  J  inch  from 
the  true  contour.  At  Sioux  City, 

la.,  the  surface  is  worked  to  a  pasty  mass  by  long-handled  wooden 
floats,  Fig.  146.  The  floats  are  14X16X2  inches.  The  con- 
crete is  laid  wet  and  worked  smooth.  Then  a  dry  mixture  of 


276 


CONCRETE  ROADS 


equal  parts  of  cement  and  sand  is  sprinkled  on  the  surface  to 
absorb  the  surplus  water.     The  floating  is  continued  until  the 


FIG.  147. 


pasty  adhesive  mass  is  slightly  drown  along  with  the  float. 
The  resulting  surface  is  rough  but  not  sharp. 


n 


PLAN  OF  rf*j[Borimn 

ROLLER  FOR  FINISHING  SURFACES  VS\ 
OF  CONCRETE  ROADS  AND  STREETS          \  \ 

L  (JGo/v:  me  fa/  p/ofe 


~3Cut  washers 


Hood  heads 
spked  together 
Crossing  fne  grain 


FIG.  148. 

A  Canvas  or  Rubber  Belt  from  6  to  12  inches  wide  with  sticks 
nailed  across  the  ends  for  handles  is  used  for  finishing  by  having 


REINFORCING  277 

a  man  on  each  side  of  the  roadway  take  the  belt  by  the  handles 
and  see-saw  it  along  the  pavement.  A  Light  Roller  may  be 
drawn  by  means  of  long  handles  or  ropes  backward  and  for- 
ward over  the  pavement.  It  compresses  the  concrete,  reduces 
the  voids  and  forces  out  surplus  water,  Figs.  147,  148.  Wood 
Tamping  Templates,  Fig.  149,  for  one  or  two  men  are  employed. 
Reinforcing. — In  case  it  is  thought  necessary  to  place  rein- 
forcing, and  this  is  frequently  done  when  the  pavement  is  more 
than  20  feet  wide,  it  is  placed  not  less  than  2  inches  from  the 
finished  surface  and  extends  to  within  2  inches  of  all  joints,  but 
should  not  cross  them.  The  adjacent  widths  of  fabric  are  to  be 
lapped  not  less  than  4  inches.  The  reinforcing  fabric  may  be 
either  woven  wire  or  expanded  metal,  but  the  cross-sectional 


FIG.  149. — Wood  Tamping  Templates  and  Light  Bridge  for  Furnishing 
Concrete  Roads. 

area  running  parallel  to  the  center  line  of  the  roadway,  accord- 
ing to  standard  specifications  should  amount  to  at  least  0.038 
square  inch  per  foot  of  pavement  width,  and  the  cross-sectional 
area  of  reinforcing  which  is  perpendicular  to  the  center  line  of 
the  roadway  should  be  at  least  0.049  square  inch  per  foot  of 
pavement  length. 

Curing  and  Protection. — Concrete  must  be  kept  damp  for 
some  time  after  depositing  in  order  to  harden  properly.  Spray- 
ing or  sprinkling  as  soon  as  it  is  hard  enough  not  to  pit  is  rec- 
ommended unless  the  temperature  should  be  below  50°  F., 
when,  in  the  discretion  of  the  engineer,  it  may  be  omitted.  In 
warm  sunshiny  weather  a  canvas  placed  over  the  new  pave- 
ment until  it 'is  hard  enough  to  be  covered  is  customary.  As 
soon  as  permissible  the  roadway  should  be  covered  with  earth 
about  2  inches  deep;  this  is  allowed  to  remain  on  the  road  for 


278  CONCRETE  ROADS 

about  ten  days  or  two  weeks  and  kept  moist.  Traffic  should 
not  be  allowed  on  the  road  until  the  pavement  is  well  cured. 
Two  weeks  in  warm  weather  and  longer  in  cool  weather  is  the 
minimum.  A  month  is  much  better. 

The  method  of  ponding  is  a  common  practice  in  California. 
Shallow  earth  dams  are  placed  along  the  edge  and  across  the 
pavement;  the  small  ponds  or  reservoirs  thus  formed  are  filled 
with  water.  Excellent  results  are  reported  from  this  method  of 
curing. 

Freezing  Weather. — Although  some  people  think  concrete 
can  without  injury  be  deposited  in  freezing  weather,  the  best 
practice  is  not  to  permit  it.  And  even  if  the  temperature  gets 
nearly  to  freezing,  the  aggregates  and  water  should  be  heated 
before  mixing,  and  precautions  taken  to  protect  the  work  from 
freezing  for  at  least  ten  days.  Straw  and  manure  have  been 
used  successfully  for  protection. 

Two-course  Work. — With  two-course  work  the  only  prac- 
tical difference  is  that  the  lower  course  may  be  made  leaner  and 
the  wearing  surface  is  made  of  finer  stone.  Standard  specifica- 
tions require  for  the  foundation  course  1  bag  of  Portland  cement 
to  not  more  than  2J  cubic  feet  of  fine  aggregate  (passing  J-inch 
screen),  and  not  more  than  4  cubic  feet  of  coarse  aggregate 
(passing  IJ-inch  screen,  retained  on  J-inch).  The  leanest 
allowable  then  is 

cement  :  sand  :  stone  =  1  :  2 J  :  4. 

The  wearing  course  consists  of  two  parts  material  specified  above 
as  fine  aggregate  and  three  parts  clean,  hard  durable  crushed 
rock  or  gravel,  free  from  dust,  soft  particles,  loam,  vegetable,  or 
other  deleterious  matter,  and  passing  when  dry  a  screen  having 
J-inch  openings  and  retained  on  a  screen  having  J-inch  openings. 
The  mortar  is  to  be  mixed  in  the  proportions  of  1  bag  of  Port- 
land cement  and  not  more  than  2  cubic  feet  of  aggregate  for 
wearing  course  just  described.  That  is  a  mixture  of 

1  cement  :  2  wearing  course  aggregate  = 
1  cement  :  4/5  sand  :  6/5  small  stone. 


EXPANSION  JOINTS  279 

A  cubic  yard  of  lower  course  in  place  should  contain  at  least  1.4 
barrels  (5.6  bags)  of  cement;  and  a  cubic  yard  of  wearing  sur- 
face, 2.97  barrels  (11.9  bags). 

It  is  not  necessary  to  strike  off  the  lower  course  with  a 
template.  The  concrete  is  deposited  to  approximately  the 
thickness  of  the  wearing  course  below  the  grade  line  of  the 
finished  surface. 

Expansion  and  Contraction  Joints. — Just  how  frequently 
expansion  joints  should  be  placed  is  a  matter  on  which  there  is 
considerable  difference  of  opinion.  Some  think  every  200  or 
300  feet  is  sufficient;  others  say  every  30  to  50  feet.  Recom- 
mended practice  1  would  place  them  not  more  than  50  feet 
apart  transversely  and  along  each  curb.  In  California,  where 
the  range  of  temperature  is  considerably  less  than  in  most  of  our 
Northern  States,  miles  of  roadway  are  constructed  without  any 
expansion  and  contraction  joints.  When  they  have  a  well- 
drained  and  compacted  subgrade  they  give  no  trouble  what- 
ever. The  standard  width  of  the  joint  is  one-fourth  inch. 
Joint  filler  made  of  tarred  felt  which  may  be  placed  in  position 
before  the  concrete  is  deposited  is  now  on  the  market.  Where 
such  cannot  be  obtained  a  well-greased  sheet  of  steel  is  set  in 
the  joint  until  the  concrete  is  hard,  then  removed  and  the  joint 
filled  with  heavy  tar  or  hot  asphalt.  Care  must  be  taken  that 
the  tarred  felt  or  sheet  of  steel  is  secured  against  deflection. 
The  joint  should  remain  a  true  vertical  plane  to  prevent  the 
tendency  of  one  section  rising  above  the  other. 

Joint-protection  Plates. — An  effort  to  prevent  the  chipping 
of  the  concrete  at  the  joint  edge  has  led  to  several  kinds  of  joint 
protection.  The  tendency  of  present  practice,  according  to 
the  second  "  Concrete  Road  Conference,"  Chicago,  1916,  is 
toward  the  omission  of  metal  protection  plates  for  joints.  It  is 
possible  that  their  value  depends  somewhat  on  the  character 
of  the  aggregate  used,  and  it  is  considered  that  they  are  more 
essential  in  street  pavements  than  in  country  highways.  Metal- 
lic joint-protection  plates  are  usually  made  of  steel  securely 
anchored  to  the  concrete.  But  even  such  are  not  entirely 

1  National  Conference  Concrete  Road  Building,  1914  Proceedings. 


280  CONCRETE  ROADS 

satisfactory  because  the  steel  does  not  wear  down  at  the  same 
rate  as  the  concrete.     An  uneven  surface  results,  which  eventu- 


FIG.  150. — Kahn  Armored  Joint. 


FIG.  151. — Machine  for  Placing  Expansion  Joint. 

ally  becomes  a  pot  hole  or  rut.     Fig.  150  shows  one  of  the  forms 
on  the  market.     Special  devices  are  made  for  installing  fillers, 


EXPANSION  JOINTS 


281 


.Width.Utt.than.lO.feet 
Are  of  Circle 


Concrete^ 


Woaring  course  net  leu  than  2 
Base  nut  lest  than  6 
Nott  "  W  "denoM  width  of  pavement     ., 
*  Except  at  noted  in  ^.ccijicativnt     X  Longitudinal  J»int 


f  k  Longitudinal  Joint 

Kote  "  W"denotet  width  of  pavement 
*  Except  as  noted  in  Specification* 


FIG.  152.     Typical  Concrete  Road  and  Street  Cross-sections  with 
Curb  and  Gutter. 


Typical  Section  of  Concrete  Roadway. 

Side  ditches  should  be  of  sufficient  size  to  dispose  of  all  drainage;  C  may  vary  from 

W       W 

—  to  — ,  when  w  exceeds  20  feet  make  joint  in  center  and  crown  subgrade;   k  varies  from 

96       72 

6  to  12  inches. 


Commonwealth  Avenue  Road,  Duluth 
FIG.  153. — Typical  Concrete  Road  Cross-sections. 


282  CONCRETE  ROADS 

Fig.  151.  By  these  the  joint  filler,  a  tarred  felt,  with  or  without 
the  plates,  are  held  securely  in  place  and  free  from  deflection 
while  the  concrete  is  being  deposited. 

Cross-section. — Figs.  152,  153,  show  recommended  cross- 
sections  for  concrete  roadways.  The  thickness  is  controlled  by 
several  factors,  such  as  the  character  and  drainage  of  the  sub- 
grade,  the  character  and  amount  of  the  traffic,  the  width  and 
crown  of  the  roadway.  Drainage  and  consolidation  of  sub- 
grade  are  extremely  important  items  in  all  road-making  and 
no  less  so  under  a  concrete  pavement.  Unequal  settlement  is 
sure  to  produce  a  cracked  surface.  With  better  roads  will 
naturally  come  an  increased  use  of  heavy  motor  trucks  and 
tractors.  The  thickness  must  be  such  that  the  concrete  will 
not  break  under  the  heaviest  load.  It  is  recommended  that 
roads  having  a  crown  be  made  thicker  in  the  middle  than  on  the 
edges;  while  roads  with  an  inverted  crown  (lower  in  the  middle 
than  on  the  sides)  used  in  alleys  and  in  narrow  cuts  where  rain- 
water is  liable  to  wash  out  the  side  ditches,  and  those  on  side 
hills  with  the  slope  all  in  one  direction,  be  made  the  same 
thickness  throughout.  Practice  seems  to  vary  from  5  to  8 
inches.  The  concrete  Road  Conference  recommends  a  mini- 
mum of  6  inches.  An  analysis  of  the  statistics  of  paving 
construction  for  1915  published  in  "  Engineering  and  Con- 
tracting," April  5,  1916,  will  show  that  of  125  different  localities 
covering  the  entire  United  States, 

50  places,  40.0  per  cent,  constructed  concrete  pavements  6  inches  thick. 
49  places,  39.2  per  cent,  constructed  concrete  pavements  7  inches  thick. 
10  places,  8.1  per  cent,  constructed  concrete  pavements  8  l  inches  thick. 

6  places,    4.8  per  cent,  constructed  concrete  pavements  5    inches  thick. 

5  places,  4.0  per  cent,  constructed  concrete  pavements  6£  inches  thick. 
1,  6i  1,  7i;  and  2,  7|  inches  thick. 

Width. — A  desirable  width  of  pavement  for  a  single-track 
roadway  is  10  feet;  for  double-track  roadway  20  feet.  In  case 
of  a  single-track  roadway  an  earth  roadway  of  equal  width  or 
shoulders  of  5  feet  each  should  be  kept  alongside.  For  a 

1  Several  of  these  were  thinner  at  the  outside  edges,  as  thin  as- 6  inches. 


MAINTENANCE 


283 


double-track  paved  way  the  shoulder  need  be  used  for  turnout 
purposes  only  in  cases  of  congestion. 

The  crown  or  slope  of  the  paved  way  should  be  not  less  than 
one-hundredth,  nor  more  than  one- 
fiftieth  its  width.     Except  in  un- 
usual cases  the  lower  crown  is  to 
be  preferred. 

Integral  Curb. — If   a   curb  is 
desired  it  may  be  constructed  as 
curbs  already  described  for  other 
pavements  or  built  integrally  with 
the  concrete.     The  latter  is  prefer- 
able.    Precaution  should  be  taken  PlG' 154' 
that  it  is  thoroughly  bonded  to  the  pavement  proper.    Figs. 
154  and  155  illustrate  integral  curbs  with  method  of  construction. 

Maintenance. — Here,  as  in  all  other  roads,  constant  atten- 
tion will  diminish  the  need  of  extensive  repairs.  The  proper 
maintenance  of  a  concrete  road  consists  in  filling  cracks  and 
potholes  as  soon  as  possible  after  their  appearance.  In  Wayne 
County,  Michigan,  a  crew  consisting  of  seven  men  and  a  team 


TYPICAL  CROSS  SECTION  OF  CONCRETE  GUTTER  AND  DESIGN  FOR  A  TEMPLATE 
TO  BE  USED  IN  ITS  CONSTRUCTION. 

FIG.  155. 

is  utilized  for  maintaining  their  numerous  concrete  roadways.1 
A  foreman  is  paid  $5  a  day,  the  team  and  driver  $5  a  day,  the 
"  tar  man  "  $3  a  day,  two  laborers  at  $2.50  each,  and  two 
laborers  at  $2.25  each.  The  tools  used  are  two-wire  bristle 
brooms,  a  wheelbarrow,  a  couple  of  shovels  and  a  tar  bucket 
with  a  round  spout.  The  cracks  are  swept  clean  with  the  wire 

Report  of  Committee  VI.     Edward  N.  Hines,  Chairman,  Proceed- 
ings National  Conference  on  Concrete  Road  Building,  Chicago,  1914,  p.  110. 


284  -CONCRETE  ROADS 

brooms  and  filled  with  a  heavy  tar  (Tarvia  X)  at  225°  F.  An 
excess  of  tar  is  poured  so  that  it  extends  beyond  the  edge  of  the 
crack.  After  standing  a  few  minutes,  dry,  coarse  sand  is 
spread  with  a  shovel  over  the  crack  and  into  the  tar ;  this  is  left 
for  the  traffic  to  iron  out.  The  excess  tar  is  worn  away,  leaving  a 
smooth  even  surface.  The  work  is  preferably  done  on  hot,  dry 
days,  and  once  a  year,  they  think,  often  enough  to  go  over  the 
work.  Small  pot-holes  are  treated  in  the  same  manner.  Of 
course,  asphalt  may  be  used  in  place  of  tar. 

Repairs. — In  case  of  large  pot-holes  or  places  removed  for 
water  pipes,  telephone  conduit  or  other  purposes,  more  extensive 
repairs  than  those  mentioned  in  the  report  will  be  necessary. 
The  edges  of  the  concrete  should  be  trimmed  to  make  the  walls 
vertical,  the  subsoil  carefully  replaced  and  tamped.  Concrete 
of  the  same  character  as  the  original  roadway  is  used  to  fill  the 
opening  and  then  finished  as  before.  In  time  cracks  may  appear 
between  the  new  concrete  and  the  old,  they  will  be  treated  as 
other  cracks. 

Seal  Coat  or  Carpet. — Since  a  bituminous  material  has  been 
satisfactorily  used  for  filling  cracks  and  small  holes  there  has 
arisen  the  idea  of  covering  the  entire  pavement  with  a  seal  coat, 
squeegee  coat  or  .carpet.  The  hot  bituminous  asphalt  cement, 
refined  tar,  or  tar-asphalt  is  spread  from  sprinklers  and  swept 
over  with  brooms  or  applied  with  "  squeegees."  A  thin  layer, 
|  to  J  inch,  of  coarse  sand  or  crushed  stone  screenings  is  spread 
upon  the  hot  bituminous  matter.  Sometimes  this  latter  is  rolled 
with  a  light  roller,  sometimes  not.  The  main  difficulty  has 
been  to  get  the  bituminous  coat  to  adhere  thoroughly  to  the 
concrete.  Dust  or  too  much  moisture  in  the  concrete  will  pre- 
vent. A  little  moisture  is  said  to  assist  and  a  very  light  appli- 
cation of  a  thin  oil  is  claimed  to  be  beneficial.  It  is  also  said 
that  two  applications  of  the  material  with  a  pressure  machine  of 
\  gallon  per  square  yard  each  is  better  than  a  single  application 
of  \  gallon. 

Cost  of  Concrete  Roads. — It  is  difficult  to  give  in  general 
terms  the  cost  of  a  concrete  road.  The  particular  factors  that 
enter  into  the  cost  of  the  individual  road  should  be  taken  into 


MAINTENANCE 


285 


account.  Type,  that  is,  one-course,  two-course,  bituminous 
top,  or  reinforced ;  thickness ;  location ;  extent  and  contractor's 
guarantee  are  some  of  these  factors.  Without  taking  any  of 
these  into  account  an  analysis  of  the  statistics  for  the  concrete 
pavements  constructed  in  1915  l  shows  that  of  the  136  localities 
reported,  distributed  generally  over  the  United  States,  21  per 
cent  paid  from  $1.20  to  $1.30  per  square  yard.  While  40  per 
cent  of  the  localities  come  within  the  limits  of  $1.10  to  $1.40; 
and  74  per  cent  within  the  limits  of  $1.00  to  $1.70.  The  lowest 

Shaping  Roadbed 

$  trimming 
Shoulder 


Wayne  County.  JfUUttfrtt 


A  weighted  mean  cowering 

data  from  7  Michigan  Soadt 

1912-13,  8  Wayne  County,  and 

Illinois  Roads, 


FIG.  156. — Concrete  Pavement  Costs. 

reported  price  is  $0.66  and  the  highest  $2.65  per  square  yard. 
Fig.  156  is  a  graphical  representation  of  concrete  pavement 
costs. 

Data  prepared  by  Committee  XII  of  the  National  Con- 
ference on  Concrete  Road  Building,  A.  N.  Johnson,  Chairman,2 
give  an  average  cost  of  a  one-course  concrete  road  to  be  $1.24 
and  a  weighted  average  of  $1.19.  The  diagrams  in  Fig.  156 
were  also  presented  by  the  same  committee. 

1  For  statistics  see  Engineering  and  Contracting,  April  5,  1916. 

2  Proceedings,  1914,  p.  142. 


286  CONCRETE  ROADS 

Miscellaneous  Methods.  Grouting. — The  Hassam  pave- 
ment is  made  by  placing  a  layer  of  broken  stone  ranging  in  size 
from  1 J  to  2|  inches  and  rolled  as  in  macadam  construction  to  a 
thickness  of  4  inches.  A  grout,  1  part  cement  to  3  parts  sand, 
is  poured  over  this,  care  being  taken  continually  to  agitate  the 
grout,  in  order  to  prevent  segregation,  until  deposited.  Rolling 
is  continued  during  the  pouring  of  the  grout  to  force  it  into  the 
interstices  of  the  stone.  When  the  voids  are  filled  a  second 
course  of  broken  stone  is  laid.  This  may  be  of  a  harder  tougher 
rock  and  about  2  inches  thick.  It  is  grouted  and  rolled  but 
with  a  thinner  grout,  1:2.  The  surface  is  finished  by  brooming 
and  brushing*into  it  a  thick  grout  composed  of  1  part  cement, 
1  part  sand  and  1  part  pea-size  trap  rock.  This  process  is 
patented. 

Oil-cement  Concrete. — Fluid  residual  petroleum  is  added 
to  the  concrete  in  the  mixer  in  the  proportion  of  10  to  18  per 
cent  of  the  weight  of  trie  cement.  The  addition  of  oil,  while  it 
weakens  the  cement,  is  supposed  to  make  it  more  waterproof. 
Some  experimental  roads  have  been  built  but  the  process  has 
not  otherwise  been  used. 

ORGANIZATION 

As  the  cost  of  a  pavement  depends  upon  the  efficiency  of 
the  working  crew  the  following  extracted  from  Bulletin  249, 
U.  S.  Office  of  Public  Roads,  by  C.  H.  Moorefield  and  J.  T. 
Voshell,  will  be  of  interest  to  the  concrete  road  maker : 

Preliminary  Planning. — The  work  of  mixing  and  depositing 
should  be  as  nearly  continuous  as  practicable  after  it  is  once 
begun.  To  effect  this  the  order  and  progress  of  the  work  should 
be  carefully  planned  beforehand.  This  means  that  provision 
should  be  made  for  completing  the  drainage  structures,  the 
grading  and  the  preparation  of  the  subgrade  well  ahead  of  the 
mixer,  as  well  as  supplying  the  mixer  with  necessary  materials. 

The  drainage  structures  should  preferably  be  completed  in 
advance  of  the  grading.  However,  there  are  places  where  it 
will  be  more  advantageous  to  do  otherwise. 

The  work  of  preparing  the  subgrade  and  setting  the  forms 


ORGANIZATION 


287 


should  preferably  proceed  sufficiently  far  in  advance  of  the  mixer 
to  allow  for  two  or  three  days'  run.  The  prepared  subgrade  will 
usually  dry  out  more  quickly  after  a  rain  than  the  unprepared 
road.  It  may  need  re-rolling  after  a  rain. 

Selecting  the  Concrete  Mixer. — Two-size  mixers  are  in  gen- 
eral use.  The  smaller  capable  of  mixing  a  batch  containing 
two  bags  of  cement;  the  larger,  three  bags.  Where  the  mate- 
rials can  be  economically  obtained  only  at  a  slow  rate,  or  where 
the  expense  of  providing  facilities  for  handling  large  quantities 
would  be  excessive,  the  smaller  size  mixer  is  more  economical 


FIG.  157a. 


FIG.  1576. 

to  use.  Either  mixer  should  mix,  ordinarily,  from  400  to  450 
batches  in  a  working  day  of  eight  hours.  The  diagrams, 
Fig.  157,  illustrate  mixer  organizations  for  the  two  sizes  of 
mixers. 

Handling  Materials. — One  of  the  difficult  problems  to 
be  solved  is  that  of  handling  the  materials.  The  different 
kinds  of  materials  required  must  be  delivered  to  the  mixer  in 
definite  proportions  at  the  same  time;  the  location  of  the 
materials  influence  the  transportation  methods.  Consider, 
for  example,  a  "  three-bag  mixer."  If  the  work  is  to  progress 
normally,  the  quantities  of  materials  required  each  day  will  be 
approximately,  for  a  1  :  1J  :  3  mixture,  as  follows: 


288  CONCRETE  ROADS 

Cement,  barrels 320 

Sand,  cubic  yards 70 

Coarse  aggregate,  cubic  yards 140 

Water,  gallons 8800 

In  addition  to  this,  if  the  mixer  runs  continuously,  about  10,000 
gallons  of  water  will  be  required  each  day  for  keeping  wet  that 
part  of  the  pavement  which  will  have  been  laid  during  the  two 
preceding  weeks.  This  makes  a  total  weight  of  water  which 
may  be  required  each  day  of  75  tons,  and  the  total  weight  of  all 
materials  combined  of  about  420  tons  per  day, 


CHAPTER    XIII 
BITUMINOUS  ROADS 

ROAD  surfaces,  the  binding  material  of  which  is  a  cement 
composed  chiefly  of  bitumen,  constitute  an  important  part  of 
the  pavements  of  cities  and  villages,  and,  in  some  forms,  have 
extended  to  a  considerable  extent  to  rural  highways.  Since  the 
design  of  such  road  surfaces  is  a  highly  technical  operation 
requiring  much  space  for  adequate  treatment,  and  since  there 
are  many  good  books  dealing  with  the  details  of  asphalt  and 
other  bituminous  pavements,1  it  has  been  thought  best  to 
describe  the  subject  but  briefly  in  this  text. 

Materials. — Bituminous  roads  are  constructed  of  a  mineral 
aggregate  bound  together  by  a  bituminous  cement,  that  is,  one 

1  Abraham's  "Asphalts  and  other  Allied  Substances,"  D.  Van  Nostrand 
Co.,  N.  Y. 

Blanchard's  "American  Highway  Engineers'  Handbook,"  Wiley  & 
Sons,  N.  Y. 

Blanchard  and  Browne's  "Highway  Engineering,"  Wiley  &  Sons,  N.  Y. 

Baker's  "Roads  and  Pavements,"  Wiley  &  Sons,  N.  Y. 

Boorman's  "Asphalts,"  Wm.  T.  Comstock,  Chicago. 

Danby's  "Natural  Rock  Asphalts  and  Bitumens,"  Constable  &  Co., 
N.  Y. 

Hubbard's  "Dust  Preventives  and  Road  Binders,"  Wiley  &  Sons,  N.  Y. 

Hubbard's  "Highway  Inspectors'  Handbook,"  Wiley  &  Sons,  N.  Y. 

Hubbard's  "Laboratory  Manual  of  Bituminous  Materials,"  Wiley  & 
Sons,  N.  Y. 

Harger  and  Bonney's  "Handbook  for  Highway  Engineers,"  McGraw- 
Hill  Book  Co.,  N.  Y. 

Tilson's  "Street  Pavements  and  Paving  Materials." 

Richardson's  "Modern  Asphalt  Pavement,"  Wiley  &  Sons,  N.  Y. 

Whinery's  "Specifications  for  Street  Roadway  Pavements,"  McGraw- 
Hill  Book  Co.,  N.  Y. 

289 


290  BITUMINOUS  ROADS 

having  as  an  essential  constituent,  bitumen.  The  forms  in 
which  the  bitumen  occurs  bear  various  names,  the  asphalts  and 
the  tars  being  the  most  important  for  road  purposes. 

Classification. — The  sub-types  of  bituminous  roadways 
are:  (1)  Bituminous  Earth,  (2)  Bituminous  Macadam,  (3) 
Bituminous  Concrete,  (4)  Sheet  Asphalt,  (5)  Rock  Asphalt,  (6) 
Bituminous  and  Bituminized  Block. 

Definitions. — Some  terms  are  continually  recurring  in  a 
discussion  of  bituminous  roads  and  it  may  be  well  to  give  their 
technical  meaning  at  the  beginning.  Most  of  these  definitions 
have  either  been  adopted  or  have  been  proposed  by  committees 
for  adoption,  by  such  organizations  as  the  American  Society  of 
Civil  Engineers  and  the  American  Society  for  Testing  Materials. 

Bitumens. — Mixtures  of  native  hydrocarbons  and  their  non- 
metallic,  derivatives  which  may  be  gases,  liquids,  viscous 
liquids,  or  solids  and  which  are  soluble  in  carbon  disulphide.1 

Asphalts. — Solids  or  semi-solid  native  bitumens,  solid  or 
semi-solid  bitumens  obtained  by  refining  petroleum,  or  solid 
or  semi-solid  bitumens  which  are  combinations  of  the  bitumens 
mentioned  with  petroleums  or  derivatives  thereof,  which  melt 
upon  the  application  of  heat  and  which  consist  of  a  mixture  of 
hydrocarbons  and  their  derivatives.1 

Flux. — Bitumens,  generally  liquid,  used  in  combination  with 
harder  bitumens  for  the  purpose  of  softening  the  latter.1 

Asphalt  Cement. — A  fluxed  or  unfluxed  asphalt  specially 
prepared  as  to  quality  and  consistency  for  direct  use  in  the  man- 
ufacture of  bituminous  pavements  and  having  a  penetration  at 
25°  C.  (77°  F.)  of  between  5  and  250,  under  a  load  of  100  grams 
applied  for  five  seconds.1  This  is  usually  spoken  of  by  the 
workmen  as  A.C.  (See  penetration  below.) 

Rock  Asphalt. — Sandstone  or  limestone  naturally  impreg- 
nated with  asphalt.1 

Tars. — Bitumens  which  yield  pitches  upon  fractional  dis- 
tillation and  which  are  produced  as  distillates  by  the  destructive 
distillation  of  bitumens.1 

1  Report  of  Special  Committee  A.  S.  C.  E.  Proceedings,  1914;  Am.  Soc. 
for  Testing  Materials.  Year  Book,  1915. 


SOURCES  OF  BITUMENS  291 

Coal  Tar. — Tar  produced  from  the  destructive  distillation  of 
coal. 

Gas  Coal  Tar. — Tar  produced  in  the  gas-house  retorts  from 
bituminous  coal. 

Water-gas  Tar. — Tars  produced  by  cracking  oil  vapors  at 
high  temperature  in  the  manufacture  of  water  gas.1 

Pitches. — Solid  residues  produced  in  the  evaporation  or 
distillation  of  bitumens,  the  term  being  usually  applied  to  resi- 
dues produced  from  tars.1 

Refined  Tar. — Tar  freed  from  water  by  evaporation  or  dis- 
tillation, or  a  product  produced  by  fluxing  tar  residuum  with 
tar  distillate.1 

Penetration. — A  term  to  define  the  solidity  or  consistency  of 
bituminous  material.  It  is  measured  by  the  distance  expressed 
in  tenths  of  a  millimeter  which  a  weighted  standard  cambric 
needle  under  standard  conditions  will  penetrate  the  sample. 

Viscosity. — The  measure  of  the  resistance  to  flow  of  a  bitu- 
minous material,  usually  stated  as  the  time  of  flow  of  a  given 
amount  of  material  through  a  given  orifice.  This  time  of  flow 
divided  by  the  time  of  flow  of  the  same  volume  of  water  at 
25°  C.  (77°  F.)  is  designated  as  the  specific  viscosity ,  volume  and 
temperature  stated. 

SOURCES  OF  BITUMINOUS  MATERIALS 

Native  Asphalts. — Asphalts  are  found  native  as  solid  or  semi- 
solid  bitumens  in  various  places,  but  especially  in  Venezuela. 
On  the  island  of  Trinidad  is  a  pitch  lake  of  115  acres,  135  feet 
deep  at  the  center  and  on  the  mainland  the  Bermudez  lake  of 
about  1200  acres  with  a  maximum  depth  of  10  feet,  and  the 
Maracaibo  deposits  near  the  Gulf  of  Maracaibo.  Trinidad 
asphalts  contain  as  found  about  39  per  cent  bitumen  soluble 
in  carbon  disulphide;  Bermudez  and  Maracaibo  about  72  per 
cent.  When  "  refined  "  by  heating  in  kettles  to  drive  off  the 
water,  remove  floating  foreign  substances  and  reduce  to  a 

1  Report  of  Special  Committee  A.  S.  C.  E.  Proceedings,  1914;  Am. 
Soc.  for  Testing  Materials.  Year  Book,  1915. 


292  BITUMINOUS  ROADS 

uniform  consistency,  the  percentages  are  increased  for  Trinidad 
to  about  56  and  Bermudez  to  94. 

Deposits  of  native  asphalt  are  found  also  in  Cuba  (Cuban), 
California  (Alcatraz)  and  in  Utah  and  Colorado  (Gilsonite). 
Gilsonite  is  found  in  veins  and  is  about  99  per  cent  soluble 
bitumen. 

Petroleum  Asphalts. — Asphalts  are  obtained  from  refining 
the  asphaltic  oils  of  California,  Mexico,  Southern  Illinois,  Texas, 
Oklahoma,  and  Wyoming.  Eastern  petroleum  oils  have  a 
paraffin  base  with  very  little  asphalt,  the  extreme  western  oils 
have  an  asphaltic  base  with  little  paraffin,  while  those  from  the 
intermediate  districts  have  both  in  varying  degrees.  No 
asphalt  is  obtained  from  Pennsylvania  oils,  but  large  quanti- 
ties are  prepared  from  the  California  asphaltic  oils  and  the 
Texas  semi-asphaltic  oils.  The  asphalt  remains  after  the  vola- 
tile oils  have  been  distilled  off  by  use  of  saturated  steam,  or  after 
they  have  been  partially  distilled  and  the  remainder  driven  off 
by  blowing  air  through  the  residue.  The  quality  of  the  asphalt 
depends  on  the  character  of  the  crude  oil  and  also  on  the  maxi- 
imum  temperature  attained  in  the  process  of  refining.  Air 
blowing  is  claimed  to  keep  the  temperature  below  the  destructive 
cracking  or  decomposition  limit. 

Road  tars  and  pitches  are  obtained  from  the  destructive 
distillation  of  coal  in  illuminating-gas  manufacturing  plants  or 
coke  ovens.  This  tar  is  refined  by  distilling  off  the  water  and 
volatile  oils.  The  process  is  carried  only  so  far  as  is  necessary 
to  produce  the  consistency  wanted.  For  light  or  surface  tars 
the  water  only  is  removed;  for  the  heavier  tars  the  distillation 
may  be  prolonged;  for  the  very  heavy  tars  or  pitches  steam  is 
blown  through  the  kettles.  This  carries  off  the  heavier  oils  at  a 
sufficiently  low  temperature  to  prevent  damaging  the  pitch; 
also,  the  destruction  of  the  still  by  depositions  of  carbon  and 
local  heating  is  avoided. 

Various  grades  of  road  tars  are  used  as  well  as  combinations 
of  asphalts  and  tars. 


CONSISTENCY  TESTS  293 

PHYSICAL  AND  CHEMICAL  TESTS 

A  great  many  physical  and  chemical  tests  have  been  devised 
for  controlling  the  properties  of  asphalts  and  tars.  A  very  few  of 
these  will  be  mentioned.  For  detailed  methods  as  well  as  other 
tests  the  reader  is  referred  to  the  standard  tests  of  the  American 
Society  of  Civil  Engineers,  and  the  American  Society  for  Test- 
ing Materials. 

Consistency  Test-penetration  Method. — Fig.  158  shows  an 
apparatus  for  making  this  test — a  pentrometer.  It  consists  of 
a  machine  for  applying  a  weighted  needle  to  the  sample  and 
measuring  the  distance  it  pene- 
trates. A  standard  No.  2  cam- 
bric needle  weighted,  ordinarily 
with  100  grams,  is  used  and 
the  depth  of  penetration  re- 
ported in  tenths  of  a  milli- 
meter. The  sample  is  main- 
tained at  25°  C.  (77°  F.)  during 
the  test  by  keeping  it  in  an  open 
tin  box  of  prescribed  dimensions 

and  the  tin  box  completely  sub- 

,  J  FIG.  158.— Pentrometer. 

merged  in  a  glass  cup  of  water. 

The  pentrometer  is  so  arranged  that  the  weighted  needle  may  be 
employed  for  the  exact  time,  five  seconds.  When  the  result  is 
less  than  10  or  more  than  350  the  weight  and  time  are  changed 
to  200  grams  for  one  minute  and  50  grams  for  five  seconds 
respectively.  When  practical,  penetration  tests  are  made  as 
follows,  the  second  being  most  important  and  is  what  is  meant 
by  "  penetration,"  if  no  mention  is  made  of  temperature  or 
time: 

At  4°  C.  (39°  F.)  with  a  weight  of  200  grams  for  one  minute, 
At  25°  C.  (77°  F.)  with  a  weight  of  100  grams  for  five  seconds, 
At  46°  C.  (115°  F.)  with  a  weight  of  50  grams  for  five  seconds. 

The  object  of  the  test  is  to  secure  that  consistency  or  hard- 
ness which  experience  has  shown  is  required  for  a  pavement 


294 


BITUMINOUS  ROADS 


that  will  not  be  unduly  soft  in  the  summer  time  and  will  not 
crack  in  the  winter  time.  Uniformity,  an  important  element  in 
road  materials,  is  to  a  greater  or  less  degree  regulated  by  the 
test.  Other  tests  for  consistency  are  also  used,  and  especially 
for  tars  whose  surface  tension  is  so  high  the  penetration  method 
cannot  be  relied  upon. 

Consistency  by  Viscosimeter  Method. — There  are  two  vis- 
cosimeters  in  standard  use,  Fig.  159.  With  the  Engler  the  time 
required  for  a  given  quantity  of  the  material  at  a  given  tempera- 
ture to  flow  through  a  small  orifice  compared  with  the  time  it 
will  take  water  to  flow  through  the  same  orifice,  is  the  measure 


Engler 
viscosimeter. 


New  York  testing  laboratory 
float  apparatus. 


FIG.  159. — Apparatus  for  Determining  Consistency. 
(From  Bulletin  No.  38,  Office  of  Public  Roads,  U.  S.  Dept.  of  Agr.) 

of  viscosity.  The  size  and  shape  of  apparatus  and  orifice, 
temperatures,  and  charge  have  all  been  standardized.  The 
same  is  true  of  the  other  tests  herein  mentioned. 

New  York  Testing  Laboratory  Float  Test  for  Consistency. — 
This  consists  of  an  aluminum  float  or  saucer  in  the  bottom  of 
which  is  screwed  a  conical  brass  collar,  Fig.  159.  The  brass 
collar  is  filled  with  the  samples  to  be  tested  and  screwed  into 
the  float  and  the  whole  placed  on  the  surface  of  the  water  bath. 
The  plug  of  bituminous  material  becomes  warm  and  fluid  by 
the  heat  of  the  water,  which  is  maintained  at  the  temperature 
required  for  the  test,  and  is  gradually  pushed  upward  and  out 
of  the  collar.  Water  gains  entrance  to  the  saucer  and  the 
apparatus  sinks.  The  time  in  seconds,  between  placing  the 


MELTING-POINT 


295 


saucer  on  the  water  and  the  sinking  of  the  float  is  taken  as  a 
measure  of  the  consistency  of  the  material  under  examination. 
Melting-point,  Cube  Method  (Used  with  Tars). — A  small 
cube  of  the  bituminous  material  is  suspended  by  a  No.  10 
brass  wire  in  a  beaker  of  water  or  vegetable  oil  at  least  40°  F. 
lower  than  the  fusing-point  of  the  substance,  Fig.  160.  The 
water  is  gradually  warmed  and  its  temperature  noted  by  a 
thermometer  fastened  in  such  a  manner  that  its  bulb  is  just 


MOLD 


FIG.  160. — Melting-point  Apparatus 

beside  the  cube.  The  cube  has  its  bottom  edge  at  the  start 
1  inch  from  the  bottom  of  the  beaker.  Under  the  heat  of  the 
water  the  substance  will  run  down  and  when  it  has  just  touched 
the  bottom  the  temperature  of  the  liquid  is  taken  as  the  melt- 
ing-point of  the  sample. 

Melting-point,  Ring  and  Ball  Method  (Used  with  Asphalts).1 
— The  apparatus  consists  of  a  brass  ring,  f-inch  in  diameter, 
1  Proceedings  A.  Soc.  Testing  Materials,  1917. 


296 


BITUMINOUS   ROADS 


J-inch  deep,  g^-ineh  wall,  suspended  1  inch  above  the  bottom  of 
a  600  c.c.  (approximately)  beaker.  The  ring  is  filled  with  melted 
material  which  is  allowed  to  harden  and  the  excess  removed; 
then  suspended  in  the  beaker  containing  approximately  400  c.c. 
of  water  at  a  temperature  of  5°  C.  (41°  F.) ;  the  thermometer  is 
placed  on  a  level  with,  and  within  \  inch  of  the  ring;  heat  is 
applied  at  the  rate  of  5°  C.  (9°  F.)  per  minute  (the  rate  is 
important);  the  temperature  is  recorded  at  the  starting-point 
and  every  minute  thereafter  until  the  test  is  completed.  The 
softening-point  is  the  temperature  at  which  the  specimen  has 
dropped  1  inch. 

The  melting-point  is  of  value  when  the  penetration  or  grout- 
ing method  of  constructing  bituminous  macadam  is  followed. 
Too  high  a  melting-point  means  rapid  solidification  and  conse- 
quently insufficient  penetration  of  the  interstices  of  the  stone. 
Tars  for  this  purpose  should  not  have  a  melting-point  exceeding 
25°  C.  (77°  F.)  and  a  blown  oil  not  over  35°  C.  (95°  F.). 

Solubility. — This  is  considered  to  be 
one  of,  if  not  the  most,  important  tests 
of  bituminous  materials.  It  consists  in  a 
very  carefully  standardized  method  of 
determining  the  percentage  of  the  sample 
that  win  be  dissolved  in  carbon  disulphide 
(€82).  This  test  may  be  made  on  the 
original  asphalt  or  tar  or,  of  greater  im- 
portance, on  the  mixed  product  taken 
from  the  road,  Figs.  161,  162.  When 
made  on  the  mixed  product  it  shows  the 
amount  of  binding  material  in  that  product 
and  after  that  has  been  extracted  the 
aggregate  may  be  examined  for  proper 
gradation  in  size  by  sieve  analysis. 

Solubility  tests  are  sometimes  made  in  carbon  tetrachloride 
(CCU)  and  in  petroleum  naphtha.  The  former  merely  takes 
the  place  of  the  carbon  disulphide,  while  the  latter  has  a  dif- 
ferent object.  The  residue  or  insoluble  part  in  petroleum 
naphtha  is  largely  the  part  from  which  come  the  binding  prop- 


r  Coach  Crucible 

Rubber  Sand 
-Class  Funnel 


FIG.  161. — Apparatus 
for  Determining 
Soluble  Bitumen. 


FIXED  CARBON 


297 


erties  oi  asphaltic  oils  and  cements.  The  character  of  the  sol- 
uble part  is,  nevertheless,  of  interest  and  value  to  the  road- 
maker. 

Fixed  Carbon. — A  gram  of  bituminous  material  is  placed 
in  a  platinum  crucible  having  a  tightly  fitting  cover,  Fig.  163. 
This  is  heated  first  gently  then  more  violently  until  no  smoke  or 
flame  issues  from  the  crucible.  It  is  then  heated  for  seven 


(a)  (b)  (c)  (d)  (e)  (/) 

FIG.  162. — New  York  Testing  Laboratory  Extractor  for  the  Analysis  of 
Paving  Mixtures  Containing  Broken  Stone.  Five  hundred  grams  of 
the  sample  is  placed  in  the  wire  basket  (d).  About  200  c.c.  of  CS2 
is  placed  in  the  inside  vessel  (6).  -The  carbon  lamp  (16  c.  p.)  furnishes 
heat  to  evaporate  the  CS2.  Cool  water  is  circulated  through  the  cone 
(e} ,  which  is  also  the  cover.  The  evaporated  C$2  is  condensed  on  the 
cone,  drips  on  the  sample  and  dissolves  out  the  carbon;  After 
extraction  the  solvent  matter  is  burnt  to  recover  any  fine  particles 
which  may  have  passed  into  the  extract. 

minutes  in  the  full  heat  of  the  Bunsen  burner  to  drive  off  the 
most  volatile  products;  then  cooled  and  weighed;  then  ignited 
over  a  Bunsen  burner  until  only  ash  remains.  It  is  again 
weighed  and  the  difference  in  weights  represents  the  fixed 
carbon  (coke)  in  the  original  material.  Like  the  naphtha- 
insoluble  bitumen  it  is  a  measure  of  the  mechanical  stability  of 
an  oil. 


298 


BITUMINOUS  ROADS 


Other  tests  nave  been  standardized  as  follows:    Specific 
gravity,  flash  point,  loss  on  evaporation,  distillation,  ductility 
and  paraffin.     The  character  of  these  tests 
are  indicated  by  their  names. 

BITUMINOUS  EAKTH  ROADS 

Oiled  Earth  Roads. — Some  engineers 
look  upon  oiling  earth  roads  merely  as  a 
means  of  mitigating  the  dust;  others,  as  a 
means  of  maintenance.  Since  the  construc- 
tion of  oiled  roads  consists  mainly  in  dis- 
tributing oil  upon  the  road  surface  in 
place,  their  description  will  be  deferred 
until  the  next  chapter,  which  deals  with 
FIG.  163.— Apparatus  surface  treatments. 

for    Determining        Bituminized   Earth   Roads. — A   method 
Fixed  Carbon.         of  heating,  pulverizing,  mixing  with  asphalt 
(From    Bulletin   No.  cement    an(j  laying  clay  or   loam   upon  any 
38,  Office  of  Public       -,11  i      f         i    , .  , 

T?    A    TT  Q  r^  +  suitably    prepared    foundation    has    been 
Koaas,  u.  fc.  uepi.  • 

Of  Agr.)  developed   and  patented  and  employed  on 

roadways  under  the  trade  name  of  National 
Pavement.  The  clay  or  loam,  which  may  be  taken  from 
the  roadway  in  grading,  is  placed  in  a  specially  designed 
machine  which  dries,  beats  and  thoroughly  pulverizes  it.  The 
finely  divided  particles  presenting  a  large  surface  to  be  covered 
with  cement  can  absorb  a.  greater  quantity  of  asphalt,  it  is 
claimed,  than  any  other  type  of  pavement.  When  the  beaten 
clay  is  heated  with  the  asphalt  it  is  said  to  resemble  a  pul- 
verized rock  mixture.  The  hot  material  (200  to  300°  F.)  is 
hauled  to  the  roadway  and  dumped  on  a  spot  outside  the  space 
on  which  it  is  to  be  spread,  shoveled  into  place  and  uniformly 
spread  by  raking  with  hot  rakes.  It  is  then  compressed  by 
light  rolling  or  tamping.  The  rolling  is  continued  with  a  roller 
weighing  not  less  than  260  pounds  per  inch  of  width  of  tread 
at  a  rate  of  not  more  than  200  square  yards  per  hour  per  roller, 
until  a  satisfactory  compression  is  obtained.  This  type  of 


BITUMINIZED  SAND  299 

roadway  has  not  been  in  use  sufficiently  long  to  afford  a  definite 
statement  of  durability. 

Bituminized  Sand. — The  Massachusetts  Highway  Com- 
mission has  constructed  a  number  of  miles  of  roadway  by  mixing 
by  hand  or  in  a  suitable  machine,  hot  local  sand  with  oil  asphalt 
and  then  spreading  the  mixture  on  the  prepared  roadway.  The 
pavement  has  a  thickness  of  about  4  inches  at  the  middle  and 
3  inches  at  the  sides  of  an  18-foot  roadway.  The  asphalt 
finally  adopted  was  an  oil-asphalt  having  a  penetration  of  80 
(a  penetration  of  not  less  than  60,  or  viscosity  of  500  seconds 
at  100°  C.,  Lawrence  Viscosimeter,  is  specified).  The  sand  is 
to  be  clean,  sharp,  and  fairly  coarse,  not  over  52  per  cent  passing 
a  50-mesh  sieve.  The  amount  of  oil  used  is  as  ordered,  but  not 
less  than  15  gallons  nor  more  than  20  gallons  per  cubic  yard  of 
loose  sand.  The  temperature  of  the  oil  as  used  varies  according 
to  its  nature  from  121  to  191°  C.  The  hot  mixture  is  dumped 
at  one  side,  shoveled  to  place  and  spread  uniformly  by  rakes; 
after  cooling  it  is  compressed  by  rolling  with  a  horse  roller, 
weighing  about  1  ton.  The  surface  during  the  rolling  is  shaped 
with  a  road  machine  or  other  scraper  and  finally  rolled  with  a 
steam  tandem  roller.  After  the  sand  and  oil  mixture  has  been 
shaped  and  rolled  a  seal  coat  of  asphaltic  oil  is  distributed  with  a 
pressure  distributor  on  the  surface  in  two  applications  of 
J  gallon  per  square  yard.  Each  application  is  covered  with 
a  thin  layer  of  sand  and  rolled  in. 

The  Layer  Method  of  Construction. — By  this  method  about 
f  gallon  of  a  light  grade  of  oil  which  will  continue  to  mix  with 
the  sand  during  the  summer  weather  was  used  per  square  yard 
of  surface,  and  immediately  covered  with  J  inch  of  sand.  On 
this  a  second  f  gallon  of  oil  was  applied  followed  by  a  second 
J-inch  coating  of  sand.  After  this  had  thoroughly  soaked  in 
the  roadway  was  reshaped  and  a  third  application  of  oil,  • 
J  gallon,  was  made,  upon  which  was  spread  1  inch  of  sand.  The 
final  application  was  thought,  by  the  Massachusetts  Com- 
mission, to  give  better  results  if  applied  after  the  road  had 
been  used  through  a  winter. 

Bituminized  sand  roads  are  suitable  for  light  traffic  only 


300  BITUMINOUS  ROADS 

and  must  be  constantly  looked  after,  for  when  once  started  they 
very  quickly  go  to  pieces.  Better  results  were  obtained  when 
the  sand  subsoil  had  been  hardened  by  an  application  of  loam 
or  clay. 

Bituminized  Gravel. — The  fact  that  gravel  has  a  very  small 
interlocking  property  but  depends  almost  wholly  for  its  sta- 
bility on  the  cement,  natural  or  artificial,  filling  the  interstices, 
makes  it  rather  unsuitable  for  a  bituminous-bound  roadway. 
Unless  the  gravel  is  very  cheap  in  comparison  with  broken 
stone  it  will  hardly  pay  to  use  it.  When  used  it  is  recom- 
mended that  more  than  95  per  cent  should  pass  the  1-inch 
screen  and  less  than  15  per  cent  the  J-inch  screen.  A  seal  coat 
should  be  applied. 

BITUMINOUS  BROKEN-STONE  ROADS 

Broken-stone  roads  bound  together  by  bitumen  may  be 
differentiated  by  the  manner  in  which  the  cement  is  applied. 
Those  in  which  the  wearing  surface  is  laid  like  a  macadam 
roadway  and  filled  by  "  penetration  "  are  designated  as  bitumi- 
nous macadam;  those  in  which  the  stone,  or  other  mineral  aggre- 
gate, is  incorporated  with  the  cement  by  mixing  similar  to 
cement  concrete  are  defined  as  bituminous  concrete. 

BITUMINOUS  MACADAM 

Drainage  and  Foundation. — These  items  require  the  same 
attention  as  for  a  water-bound  macadam  or  any  other  type  of 
pavement.  If  the  roadway  is  to  carry  heavy  trucks,  a  cement 
concrete  foundation  of  sufficient  thickness  should  be  provided. 

The  mineral  aggregate  should  be  composed  of  good  mac- 
adam stone  subscribing  to  tests  according  to  the  traffic;  a 
coefficient  of  wear  of  not  less  than  5  for  light,  and  not  less  than 
10  for  heavy;  and  a  toughness  (impact)  of  not  less  than  5  for 
light,  and  not  less  than  10  for  heavy.  The  stones  interlock 
best  when  angular  and  are  strongest  when  length,  breadth  and 
thickness  are  approximately  equal.  The  following  stipula- 
tions were  recommended  by  the  conference  of  State  Highway 
Testing  Engineers  and  Chemists  and  published  by  the  U.  S, 


SPECIFICATIONS  301 

Office  of  Public  Roads,  and  are  here  given  not  to  be  used 
generally  but  as  a  guide  for  making  up  proper  specifications: 

General. — The  broken  stone  shall  consist  of  angular  fragments  of  rock 
excluding  schist,  shale,  and  slate,  of  uniform  quality  throughout,  free 
from  thin  or  elongated  pieces,  soft  or  disintegrated  stone,  dirt  or  other 
objectional  matter  occurring  either  free  or  as  a  coating  on  the  stone. 

Physical  Properties. — The  stone  shall  meet  the  following  requirements: 
French  coefficient  of  wear,  not  less  than  7.  (Toughness,  Hardness  and 
Absorption  may  be  added  if  desired.) 

Chips. — That  portion  of  the  product  of  the  crusher  which,  when  tested 
by  means  of  laboratory  screens,  will  meet  the  following  requirements: 

Passing  1-in.  screen,  not  less  than 95% 

Retained  on  £-in.  screen,  not  less  than 85 

Coarse  Stone. — That  product  of  the  crusher  which,  when  tested  by 
means  of  laboratory  screens,  will  meet  the  following  requirements: 

Passing  2-in.  screen,  not  less  than 95% 

Total  passing  Ij-in.  screen 25  to  75 

Retained  on  1-in.  screen,  not  less  than 85 

Alternate  Type  Specifications. — When  several  kinds  of 
materials  are  available  and  for  good  results  these  materials 
require  different  treatments  it  is  becoming  customary  to  write 
a  separate  set  of  specifications  to  cover  the  use  of  each.  This 
is  done  for  two  reasons:  (1)  To  insure  uniformity;  (2)  To 
secure  the  widest  possible  competition.  Uniformity  is  a  very 
important  factor  entering  into  the  durability  of  a  paved  road- 
way. Without  it  the  wear  is  uneven,  and  unevenness  itself 
increases  wear,  hence  with  lack  of  uniformity  deterioration 
proceeds  in  geometric  ratio.  To  make  a  blanket  specification 
to  cover  all  materials  would  result  in  one  so  open  that  uniform- 
ity would  not  necessarily  be  secured.  To  make  a  single 
specification  so  close  as  to  secure  uniformity  with  a  given  class, 
sort,  kind,  grade  or  type  of  material  might  keep  out  other 
equally  desirable  materials  and  thus  limit  competition  to  that 
person  or  those  persons  having  access  to  the  one  kind  of  mate- 
rial. By  writing  separate  specifications  for  the  several  mate- 
rials uniformity  is  insured  no  matter  which  one  is  finally  ac- 
cepted and  the  fullest  competition  is  encouraged. 


302  BITUMINOUS  ROADS 

Specifications  for  Bituminous  Cement.1 — The  following 
points,  or  so  many  of  them  as  are  applicable  or  desirable  ^to 
secure  uniformity  of  product,  are  usually  covered  by  the 
specifications: 

1.  Homogeneity. — "The  asphalt  cement  (refined  tar)  shall  be  homoge- 
neous and  shall  not  foam  when  heated  to  .  . .  V 

2.  Specific  Gravity.— Usually  taken  at  25°  C.  (77°  F.)  for  both  sub- 
stance and  water. 

3.  Melting-point. — Method  to  be  stated — cube  or  ring  and  ball. 

4.  Flash  Point. — " not  less  than °. " 

5.  Consistency. — The  penetration  method  is  ortjinarily  used  for  asphalts 
for  viscosimeter  and  float  methods  for  soft  asphalts,  tars,  and  petroleum 
oils.     Temperatures  are  specified  for  which  the  tests  shall  be  made. 

6.  Volatility. — "  Loss  by  distillation  at  ....  °  for  ....  hours  not  over 

per  cent."     The  penetration  and  specific  gravity  of  the  residue  are 

also  specified. 

7.  Solubility. — (A)  Carbon  disulphide.     "The  total  bitumen  soluble  in 
carbon  disulphide  shall  be  not  less  than  ....  per  cent." 

(a)  Organic  matter  insoluble,  not  over ....  per  cent. 

(b)  Inorganic  matter  insoluble, per  cent  to per  cent 

(B)  Carbon  tetrachloride.     Per  cent  soluble  in. 

(C)  Paraffin  naphtha.     Per  cent  insoluble  in  86°  B.  naphtha to 

8.  Fixed  Carbon.     ".,;,.  per  cent  to. ...  per  cent." 

9.  Ductility.     "....*  C.  not  less  than. . .  .centimeters." 

Occasionally  other  tests  may  be  specified. 

The  following  table  shows  a  number  of  typical  specifications: 

CONSTRUCTION 

The  subgrade,  drainage  and  foundation  course  require  the 
same  careful  attention  as  for  any  other  type  of  pavement.  In 
fact,  since  the  bituminous  cement  is  plastic  and  the  surface  will 
bend  to  fit  any  depression  that  may  come  in  its  supporting 
course,  there  is  practically  no  bridging  property  in  the  upper 
course.  Modern  practice  prefers  cement  concrete  foundations 

1  Tentative  or  standard  specifications  have  been  issued  by  such  authori- 
ties as:  The  Office  of  Public  Roads,  Dept.  of  Agriculture,  Washington, 
D.  C.;  The  American  Society  for  Municipal  Improvements;  The  American 
Society  of  Civil  Engineers;  Several  State  Highway  Departments;  and 
the  American  Society  for  Testing  Materials. 


CONSTRUCTION 


303 


tf 


U 


a      as 


Is 


Re 


a    a 


O 


a 


^  a 

d  d 


O 


O 


|S' 

ft 

l~, 


i 


Asp 


C 

Suitable  for 
Mexican  Oil 
Asphalt 


O 


O     ^ 


.2o 

+2  CO 

2V 

I* 


lt 

or  Cal 
and 
Oil 
ts 


Asph 
B 
Suitable  f 
ifornia 
Texas 
Aspha 


d   2 


-<     O  d 


.so 

+-*  rH 
2V 

I* 


d 

o 
CO 

CO 


bb 


a 

* 


IQ 


Penetration  o 
residue  not 
than  \  origi 


it 

3-3.3 


cc 


:d  o  c 

o  °  .2o 

o  J2  -gw 

o  S  c rH 

I"0  <N  ^    I 

•*J  ^  gg 

^  1  ^ 


CO 


netration  of 
due  not  less 
in  \  original 


304 


BITUMINOUS   ROADS 


such  as  have  been  treated  in  a  previous  chapter.  Old  mac- 
adam and  broken-stone  foundations  are  in  use.  In  wet  and 
yielding  soils  telford  or  Missouri  types  may  be  resorted  to. 
Upon  ordinary  good  subsoil,  well  drained,  coarse  macadam 
which  passes  over  a  IJ-inch  screen  and  through  a  2J-inch  screen, 
or  over  a  2J-  and  through  a  3|-inch  screen,  depending  on  the 
character  of  the  soil  in  the  subgrade,  is  spread  in  one  or  more 
courses  and  each  thoroughly  rolled  until  interlocked.  Some 


FIG.  164. — Constructing  Bituminous  Macadam  Roads. 

engineers  cover  each  course  with  screenings  and  finish  by  rolling 
wet.  These  courses  combined  will  be  from  6  to  10  inches  in 
thickness,  according  to  the  kind  and  amount  of  traffic  the  road 
is  intended  to  carry. 

Wearing  Surface. — A  number  of  different  methods  of  con- 
structing the  wearing  surface  are  in  use.  Without  going  deeply 
into  details  some  of  them  may  be  described  briefly  as  follows: 

Crusher  Run. — The  entire  product  of  the  stone  of  the  crusher, 
with  the  exception  of  the  screenings  sometimes,  is  spread  uni- 


CONSTRUCTION  305 

formly  and  rolled  lightly  to  bring  it  to  grade.  The  bituminous 
cement  properly  prepared  is  then  applied  by  hand  pouring  or 
by  mechanical  distributors,  Fig.  164,  and  the  rolling  continued 
until  the  required  compression  and  locking  of  stone  is  obtained. 
Dampening  or  oiling  the  rollers  may  be  necessary  to  prevent 
sticking.  A  thin  layer  of  stone  chippings  or  sand  is  spread 
over  the  bituminous  cement  and  rolled  into  the*  surface;  1J  to 
2J  gallons  of  bituminous  cement  is  required  per  square  yard. 

Uniform  Stone. — A  uniform  product  of  stone,  over  a  1J- 
and  through  a  2J-inch  screen,  is  used.  This  is  spread  and  rolled, 
the  cement  applied  and  covered  with  a  layer  of  fine  stone  chips 
or  of  sand,  and  the  rolling  continued  to  completion;  1J  to  2 
gallons  of  bituminous  cement  per  square  yard  is  required. 

Partially  Filled  Voids. — The  stone  of  the  wearing  course 
having  been  spread  and  smoothed  the  voids  are  partially  filled 
by  brooming  and  rolling  in  fine  materials.  Any  surplus  mate- 
rial is  swept  off  and  the  bituminous  cement  applied.  This  is 
covered  with  stone  chips  or  pea-gravel  and  thoroughly  rolled. 
One  and  one-fourth  to  two  gallons  of  bituminous  cement  per 
square  yard  is  used. 

Mechanically  Mixed  Filler. — The  stone  of  the  wearing 
course  is  spread  and  rolled  to  smooth.  The  voids  are  then 
filled  with  a  mixture  of  hot  sand  and  bituminous  cement  in 
practically  equal  parts  by  measurement.  Tar  pitch  has  been 
successfully  used  for  the  cement.  The  sand  cement  thor- 
oughly stirred  is  poured  by  hand  and  broomed  in,  after  which  a 
layer  of  stone  chips  or  gravel  is  spread  and  rolled  in. 

Sand-cement  Mastic  Layer. — A  layer  of  sand  is  spread 
loosely  upon  the  under  course  the  voids  of  which  have  been 
filled.  Upon  the  sand  is  distributed  about  1  gallon  per  square 
yard  of  bituminous  cement  and  the  stone  for  the  upper  course 
immediately  spread.  This  is  then  rolled  to  compact  it  and  to 
force  the  mastic  upward  into  the  interstices.  Bituminous 
cement  is  then  applied  to  the  surface  (1  to  If  gallons  per  square 
yard),  covered  to  a  depth  of  f  inch  with  f-inch  stone  chips  and 
rolled. 

Seal  Coat. — A  seal  coat  of  thin  bituminous  cement  is  often 


306  BITUMINOUS   ROADS 

spread  over  the  finished  surface,  covered  lightly  by  a  layer  of 
stone  chips  to  absorb  the  excess  bituminous  material,  and 
rolled.  One-third  to  one-half  gallon  per  square  yard  will  be 
required. 

Maintenance. — Pot  holes,  worn  places  or  depressions  caused 
by  the  settling  of  the  foundation  may  be  cut  out  and  filled  with 
ready-mixed  material  or  by  layers  of  broken  stone  and  bitumi- 
nous cement.  Bleeding  will  require  a  covering  of  dry  stone  chips. 
Where  there  is  insufficient  bitumen  it  should  be  sprinkled  on 
with  a  covering  of  stone  chips.  Where  there  are  several  miles 
of  roadway,  a  patrol  and  repair  gang  with  truck  and  materials 
constantly  on  the  job  will  be  found  to  give  best  results.  When 
the  continuous  method  of  maintenance  is  not  advisable,  the 
roadway  will  occasionally  have  to  be  scarified  and  new  stone 
added,  smoothed  and  rolled,  then  bituminous  cement  applied 
as  for  new  construction.  The  quantity  of  cement,  however, 
need  not  be  as  great. 

BITUMINOUS    CONCRETE 

Definition. — A  bituminous  concrete  road  is  one  whose 
wearing  surface  is  "  composed  of  broken  stone,  broken  slag, 
gravel  or  shell,  wi^h  or  without  sand,  Portland  cement,  fine  inert 
material  or  combinations  thereof,  and  a  bituminous  cement 
incorporated  together  by  a  mixing  method."1 

Classification. — The  committee  proposing  the  definition 
divided  bituminous  concrete  pavements  into  three  classes: 
(A)  Those  "  having  a  mineral  aggregate  composed  of  one 
product  of  a  crushing  or  screening  plant";  (B)  Those  "  having  a 
mineral  aggregate  of  a  certain  number  of  parts  by  weight  or 
volume  of  one  product  of  a  crushing  or  screening  plant"; 
and  (C)  those  "  having  a  predetermined  mechanically  graded 
aggregate.  ..." 

Patented  Mixtures. — Many  patents  for  mixtures  of  bitu- 
minous concrete  have  been  allowed  by  the  United  States 
Patent  Office  and  by  foreign  governments.  Some  of  these 

1  Proposed  by  a  special  committee  of  the  A.  S.  C.  E. 


BITUMINOUS   CONCRETE  307 

have  been  upheld  by  the  courts;  it  is  well,  therefore,  before 
using  bituminous  concrete  for  road  purposes  to  be  satisfied  as  to 
future  expense  for  royalties  or  lawsuits.  Blanchard  1  states  in 
effect  that  the  history  of  litigation  cases  indicates  that  the  con- 
struction of  bituminous  pavements  of  class  (A)  will  probably 
not  lead  to  litigation;  but  that  the  construction  of  unpatented 
bituminous  pavements  of  class  (B)  in  large  quantities  will 
probably  lead  to  an  infringement  suit;  and,  with  the  exception 
of  the  "  Topeka  Specification,"  the  construction  of  class  (C) 
pavements  in  large  quantities  will  usually  lead  to  litigation. 

Materials. — Broken  stone  suitable  for  water-bound  macadam 
roads  may  be  used  fo/  bituminous  concrete.  Broken  slag, 
gravel,  and  oyster  shells  have  also  been  used.  Trap  rock  and 
certain  kinds  of  slag  seem  best  suited  to  heavy  traffic.  A  stone 
having  an  abrasion  loss — French  coefficient  of  wear — not  less 
than  6  for  light  traffic  and  8  for  heavy,  and  a  toughness — impact 
— not  less  than  6  for  light  traffic  and  8  for  heavy  ought  to  prove 
satisfactory.  For  class  A  pavements  stone  that  will  pass  a 
IJ-inch  screen  such  that  from  3  to  10  per  cent  will  pass  a  J-inch 
screen,  has  been  recommended  as  suitable  in  size.  For  class  B 
pavements  one  specification  stipulates  run  of  crusher  stone 
passing  a  IJ-inch  screen,  having  not  more  than  5  per  cent  of 
dust;  clean  coarse  sand  to  be  used  as  a  filler  in  proportions  found 
necessary  to  fill  the  voids.  The  mixture  would  contain  from 
53  to  62  per  cent  stone,  30  to  37  per  cent  sand,  and  8  to  10  per 
cent  asphalt  cement.  For  class  C,  good  stone  or  slag,  sand,  and 
stone  dust  are  recommended.  The  aggregate  is  carefully  sep- 
arated into  several  different  sizes  and  recombined  according  to 
some  predetermined  formula,  the  object  being  to  obtain  the 
densest  possible  mixture  with  the  materials  at  hand. 

Bituminous  Cement. — Refined  tars  and  asphalts,  as  in  the 
case  of  bituminous  macadam,  have  been  used  singly  and  in 
combination.  Alternate  type  specifications  are  necessary  for 
the  different  classes  and  for  modifications  and  variation  of 
materials  under  the  several  classes.  The  following  table  shows 
characteristics  extracted  from  several  specifications: 

1  "American  Engineers'  Handbook,"  Wiley  &  Sons,  New  York. 


308 

BITUMINOUS   ROADS 

a 

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SPECIFICATIONS 


309 


The  following  are  six  optional  materials.  Additional  stip- 
ulations are  usually  required  for  some  of  them: 

Proportioning. — The  designing  of  a  proper  mixture  from  the 
different  sizes  of  stone  and  sand  and  bituminous  cement  is  not  an 
easy  proposition.  Some  engineers  work  out  the  mixture  by 
cut-and-try  method.  The  stone  having  been  separated  in 
various  sizes  is  remixed  in  varying  proportions  and  that  selected 
which  gives  the  densest  mixture,  as  determined  by  weighing  a 
given  volume.  Others  attempt  to  secure  by  calculation  those 
proportions  which  will  give  a  product  as  near  to  a  predeter- 
mined formula,  or  to  one  which  has  proved  to  be  satisfactory 
in  actual  use,  as  is  practicable.  Others  combine  the  two 
methods,  employing  the  second  method  for  a  trial  mix  and 
modifying  it  to  get  a  satisfactory  mixture.  The  quantity  of 
cement  which  the  aggregate  will  carry  is  determined  by  visual 
inspection  of  the  matrix,  or  by  softening  tests  in  an  oven  in  the 
laboratory.  The  inspector  will  gain  ability  to  judge  of  this 
through  experience.  The  mixture  must  be  such  that  the 
roadway  will  not  be  too  soft  in  the  summer  time  nor  so  hard  as 
to  crack  in  the  winter.  While  the  mix  for  every  job  should  be 
worked  out  on  its  own  rnerits  a  few  representative  designs  are 
given  for  purposes  of  comparison: 


-u    (3 
o    3 

| 

& 

o 
1 

'a?  03 

il 

•s 

<D 

ft     03 

i 
a 

11 

EH    on 

£  | 

CO    m 
03    § 

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£  3 

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CO 

6  °° 

n    ^ 

S3   'S 

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CO 

« 

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^  "S 

Bitumen,  %  

5-  7 

7-1  1 

8.9 

9.7 

8-10 

7-10 

7-  9| 

7-  8 

200-mesh  sieve  .  .  . 

5-11 

11.9 

8.3 

6-  8 

4-  8 

4-  7 

5-10 

100-mesh  sieve  .  .  . 

5-10 

3-10 

80-mesh  sieve  .  .  . 

14.5 

13.0 

10-30 

10-20 

15-20 

0.5-  2 

40-mesh:  sieve  .  .  . 

18-30 

18.6 

46.5 

15-30 

15-30 

3-  6 

10-mesh  sieve  .  .  . 

25-55 

18.9 

9.0 

5-40 

25-40 

24-32 

5-10 

15-30 

i-inch  screen  

1-5 

0.5-  3 

i-inch  screen  

3-10 

8-22 

19.1- 

6.0 

5.20 

15-40 

5-10 

3-20 

I-inch  screen  

30-45 

0-10 

18.1 

7.5 

9-30 

0-10 

8-12 

10-20 

15-25 

1-inch  screen  

10-25 

26-35 

1 

15-30 

Retained  on  1-inch 

\  40-60 

screen  

1-10 

36-50 

J 

0-20 

310 


BITUMINOUS  ROADS 


CONSTRUCTION 

Foundation. — Any  good  foundation  may  be  used.    Portland 
cement  concrete  is  considered  best,  but  old  macadam,  old  brick, 


.  165.— Asphalt  Mixer  (Courtesy  of  Warren  Bros.  Co.). 


FIG.  165a. — Asphalt  Ready  Mixor  (Courtesy  of  Asphalt  Retreating  Co.). 


DESIGNING  THE   MIXTURE 


311 


and  stone  block  have  been  successfully  used.  Naturally,  the 
heavier  the  traffic  the  stronger  the  foundation  required.  Of 
course  the  subsoil  and  drainage  must  always  be  taken  into 
account. 


FIG.  166. — A  Portable  Bituminous  Paving  Plant. 


FIG.  166a. — Asphalt  Pavement  Retreader  (Courtesy  of  Asphalt  Pavement 
Retreading  Co.,  Chicago). 

Mixing. — Hand  mixing  is  seldom  resorted  to  nowadays 
except  for  patching  or  where  very  small  amounts  are  to  be  laid. 
In  such  cases  the  mixing  is  done  on  a  board  with  shovels  or  hoes 


312  BITUMINOUS  ROADS 

in  a  manner  similar  to  the  mixing  of  cement  concrete,  except 
that  the  tools  work  better  if  heated.  There  are  many  types 
of  plants,  Figs.  165,  166,  for  mechanical  mixing  with  and  with- 
out heaters,  dryers,  separating  sieves  and  melting  kettles. 
Mixing  in  ordinary  cement  mixers,  as  well  as  hand  mixing, 
of  unheated  materials  can  be  done  to  advantage  only  in  warm 
weather  and  with  a  -soft  bituminous  cement.  Sometimes  the 
sand  and  stone  are  heated  by  piling  over  a  drum  in  which  a 
fire  is  kept  burning.  Special,  but  simple  furnaces,  are  also  in 
use  for  this  purpose.  The  more  elaborate  mixers  have  appli- 
ances for  heating  the  aggregate,,  separating  it  into  several  sizes, 
elevating  and  storing  these  in  suitable  bins  from  which  they  can 
be  drawn  by  gravity  into  a  hopper  scale,  the  proportions 
weighed  accurately  and  dropped  into  a  mixer,  usually  of  the 
pug  type.  Attached  to  the  same  plant,  or  a  part  of  it,  are 
large  kettles  for  heating  and  softening  the  bituminous  cement, 
with  proper  appliances  for  stirring  it  so  that  it  will  not  burn  to 
the  kettles.  Measured  portions  of  the  cement  are  poured  upon 
the  stone  in  the  mixer  and  the  whole  pugged  until  of  uniform 
consistency  when  it  is  dropped  into  a  waiting  wagon  and  hauled 
to  the  roadway. 

Temperature  of  Mixture. — In  best  practice  the  mixture  is 
required  to  be  placed  upon  the  roadway  at  a  temperature  not 
less  than  66°  C.  (150°  F.),  therefore  it  must  leave  the  plant  at  a 
somewhat  higher  temperature.  Specifications  usually  require 
this  to  be  not  less  than  135°  C.  (275°  F.)  and  not  more  than 
277°  C.  (350°  F.)  for  asphalt,  and  not  less  than  95°  C.  (200°  F.) 
and  not  more  than  135°  C.  (275°  F.)  for  refined  tar.  Any 
cement  heated  beyond  the  maximum  limits  should  be  rejected. 

Laying. — The  surface  of  the  foundation  being  thoroughly 
clean  and  dry  the  prepared  bituminous  concrete  is  hauled  and 
dumped  upon  platforms  or  upon  the  foundation  a  short  dis- 
tance from  where  it  is  to  be  finally  spread  by  hot  shovels  and 
raked  smooth  with  hot  iron  rakes.  The  usual  thickness  after 
compression  is  from  2  to  2J  inches. 

Rolling. — Immediately  after  spreading  the  bituminous  con- 
crete is  tamped  and  rolled.  The  rollers  should  weigh  from  8  to 


CONSTRUCTION  313 

12  tons  or  from  200  to  300  pounds  per  lineal  foot  of  roller. 
Rolling  should  begin  at  the  outside  and  proceed  toward  the 
center  of  the  roadway,  lapping  generously  upon  that  which  has 
already  been  rolled.  If  wide  enough  the  pavement  is  cross  and 
diagonally  rolled.  Some  builders  prefer  a  very  light  roller  for 
the  first  time  over  followed  by  an  8-ton  roller  and  finished  with  a 
12-  to  15-ton  roller.  Rolling,  or  tamping  in  places  inaccessible 
to  the  roller  should  continue  until  the  surface  shows  no  further 
compression. 

Seal  Coat. — A  seal  coat  of  asphalt  cement  is  immediately 
distributed  over  the  dry  smooth  surface  and  uniformly  spread 
by  squeegees  or  brooms.  Some  authorities  say  the  seal  coat 
should  be  made  of  the  same  kind  of  cement  as  the  body  of  the 
wearing  surface,  while  others  prefer  asphalt  cement  even  on  a 
tar  concrete.  The  cement  should  be  distributed  at  a  tempera- 
ture between  135°  C.  (275°  F.)  and  177°  C.  (350°  F.)  and 
immediately  covered  with  a  thin  layer  of  stone  chips  or  sand 
and  rolled  twice  by  the  roller.  Sowing  the  stone  chips  by  hand 
or  distributing  by  shovel  or  machine  are  practical  methods. 
In  one  machine  distributor  the  sand  falls  on  a  revolving  cone 
from  which  it  is. thrown  off  in  such  a  manner  as  to  spread  it 
quite  uniformly  over  the  surface. 

Maintenance. — An  occasional  surface  coating  of  tar  or 
asphalt  cement  and  stone  chips  will  keep  the  roadway  in  good 
condition  and  at  the  same  time  serve  as  a  dust  layer.  When, 
however,  the  roadway  has  been  broken  by  the  excessive  weight 
of  a  truck,  a  fracture  of  the  foundation,  or  cut  away  for  pipes  or 
under  repairs,  or  otherwise  disturbed,  it  may  be  necessary  to 
cut  out  the  damaged  places  and  refill  with  the  same  sort  of 
material,  preferably,  as  the  original  pavement,  or  by  cold  mix- 
tures in  layers,  tamping  them  or  leaving  them  to  be  compacted 
by  traffic.  The  cut  edges  of  the  pavement  should  be  painted 
by  bituminous  cement  before  the  patching  material  is  applied. 
In  case  cracks  appear  due  to  contraction  in  cold  weather  they 
may  be  cleaned  out  and  filled  with  hot  tar  or  asphaltic  cement. 
These  should  not  occur  if  the  original  bituminous  cement  is  of 
right  quality  and  consistency  and  receives  proper  treatment 


314  BITUMINOUS   ROADS 

throughout,  assuming,  of  course,  that  the  design  of  the  mixture 
is  correct. 

SHEET  ASPHALT 

Definition. — A  sheet  asphalt  pavement  is  "  one  having  the 
wearing  course  composed  of  asphalt  cement  and  sand  of  pre- 
determined grading,  with  or  without  the  addition  of  fine  mate- 
rial, incorporated  together  by  the  mixing  method."1  It 
usually  consists  of  three  courses,  a  foundation  of  cement  con- 
crete, a  binder  course  of  bituminous  concrete,  and  a  wearing 
course  of  asphalt  cement,  sand  and  stone-dust. 


FIG.  167. — Cross-section  of  a  Sheet  Asphalt  Pavement. 

A  =  Asphalt  wearing  surface. 

B  =  Binder  course. 

C  =  Concrete  base. 

D  —  Concrete  curb  amd  gutter. 

E  =  Cinders,  sand  or  gravel  for  drainage. 

Foundation. — Since  the  mineral  particles  in  this  type, 
Fig.  167,  of  pavement  are  fine  and  have  little  mechanical  sta- 
bility, and  since  the  bituminous  cement  is  more  or  less  viscous, 
the  surface  course  will  easily  conform  to  any  movements  of  its 
supporting  course;  therefore  it  is  absolutely  necessary  to  have  a 
strong  and  rigid  foundation  and  a  well-drained  subsoil.  A 
foundation  course  5  inches  thick  of  a  1  :  3  :  6  Portland  cement 
concrete  is  a  common  specification.  With  the  increase  of 
heavy  motor  transportation,  however,  double  this  thickness 
may  soon  be  advisable. 

Proposed  by  the  special  committee,  "Materials  for  Road  Construc- 
tion," Am.  Soc.  Civil  Engineers. 


BINDER  COURSE  315 

Binder  Course. — This  is  an  intermediate  course  of  lean 
asphaltic  concrete  which  furnishes  a  horizontal  stability  id  the 
wearing  course  and  serves  to  even  up  the  irregularities  of  the 
cement  foundation.  The  wearing  course  and  the  binder  become 
inseparably  cemented  together  in  the  finished  pavement. 
Binder  is  usually  composed  of  asphalt  cement  and  cubically 
broken  stone  or  slag  with  or  without  sand  or  other  fine  material. 
Ninety-five  per  cent  of  the  stone  should  pass  a  screen  with  cir- 
cular openings  having  a  diameter  three-fourths  the  thickness 
of  the  course;  none  of  it  should  exceed  in  largest  dimensions  the 
thickness  of  the  course.  There  are  two  types  of  binder  known  as 
open  and  closed,  the  preference  being  for  the  latter.  The  open 
binder  does  not  have  added  to  the  stone  used  sand  or  other  fine 
mineral  matter  to  help  fill  the  voids.  The  voids  are  later  closed 
during  the  process  of  laying  and  rolling  with  the  "  topping";  its 
advocates  claim  this  forms  a  more  perfect  union  of  the  two 
courses.  Closed  binder  in  order  to  reduce  voids  requires  a 
graded  aggregate.  The  following  is  recommended  in  addition  to 
the  dimensions  given  above  for  open  binder:  Passing  10-mesh 
sieve,  15  to  35  per  cent;  passing  J-inch  circular  opening  and 
retained  on  10-mesh  sieve,  20  to  50  per  cent;  total  passing 
i-inch  screen,  35  to  85  per  cent.  Advocates  of  the  closed  binder 
claim  it  is  more  economical  and  just  as  good.  Old  asphalt 
surfaces  have  been  used  for  the  filler,  new  asphalt  cement  being 
added  in  sufficient  quantity  to  cover  each  particle. 

The  binder  is  hauled  to  the  work  and  spread  while  hot  so 
that  it  will  roll  to  the  required  thickness,  1  to  1J  inches.  The 
upper  surface  of  the  rolled  binder  should  be  approximately  par- 
allel to  the  surface  of  the  finished  pavement.  General  traffic 
should  not  be  allowed  on  the  binder  course,  neither  should  any 
great  amount  of  time  intervene  between  its  laying  and  that  of 
the  wearing  course. 

Wearing  Course. — This  course  consists  of  asphaltic  cement 
and  mineral  aggregate.  The  cement  is  prepared  by  fluxing 
native  or  petroleum  asphalt  with  residues  from  distillation  of 
petroleum  oils  or  with  heavy  oils.  The  suitable  fluxes  vary 
so  much  that  a  definite  statement  of  proportions  would  be 


316 


BITUMINOUS   ROADS 


TS    '       ^ 

-si 


if 


GG 


^  + 


+ 


^  +  S  S  i 


10     rH 

O 


CO 


** 
A 


111! 

Is; 


rtt 

O5       •   (N 


1    ,  4-  1 
" 


WEARING  COURSE  317 

impossible.  Each  case  should  be  worked  out  by  trial  mixes  in 
the  laboratory,  and  varied  at  the  plant  as  occasion  may  require. 
The  mineral  aggregate  consists  of  graded  sand  according  to  a 
predetermined  formula  and  impalpable  dust.  The  design  of  the 
mixture  that  will  be  sufficiently  hard  and  stable  in  hot  weather, 
will  not  crack  in  cold  weather,  is  non-volatile  in  hot  weather, 
and  will  not  disintegrate  rapidly  in  wet  weather  requires  an 
expert  knowledge  of  the  theory  of  bituminous  pavements,  the 
character  and  properties  of  the  several  ingredients  used,  and 
the  best  construction  practice.  There  is  not  space  here  to  go 
into  these  matters  and  brief  mention  only  can  be  made. 

Typical  Specifications. — The  table,  p.  316,  shows  some  of 
the  important  characteristics  required  by  typical  specifications. 

Mineral  Aggregate. — Since  approximately  90  per  cent  of 
the  wearing  course  of  a  sheet  asphalt  pavement  is  made  up  of 
sand  and  stone-dust  the'  character  and  grading  of  the  mineral 
aggregate  is  an  important  element. 

Sand. — The  sand  used  should  be  clean  and  moderately 
sharp.  Some  authorities  l  prefer  a  rounded  grain,  as  it  seems 
to  compress  better  than  the  sharp.  Quartz  and  feldspar  sands 
are  to  be  preferred.  It  is  important  that  a  large  percentage  of 
the  grains  should  be  small,  but  some  coarse  grains  are  highly 
desirable.  The  researches  of  many  students  of  bituminous 
paving  have  led  to  standard  designs,  p.  318,  for  sheet  asphalt 
sand  gradings,  which  are  to  be  used  with  such  modifications 
as  may  be  demanded  by  local  materials  and  conditions. 

Filler. — A  very  fine  powder  is  used  to  fill  the  voids  of  the 
sand.  This  mixes  with,  absorbs  and  holds  the  asphalt  cement, 
possibly  because  it  greatly  increases  the  surface  area  of  the 
mineral  aggregate  to  be  painted.  The  asphalt  cement  is 
permanently  held  by  adhesion  and  does  not  act  as  a  lubri- 
cator and  the  pavement  as  a  whole  becomes  hard  and  un- 
yielding. Limestone  dust,  having  large  adhesive  power  for 
asphalt  cement,  is  commonly  used.  Portland  cement,  or 
Portland  cement  combined  with  limestone  dust,  is  by  some 

1  Richardson's  "Modern  Asphalt  Pavement,"  Wiley  &  Sons,  New 
York, 


318  BITUMINOUS  ROADS 

STANDARD  GRADINGS  OF  SAND  FOR  SHEET  ASPHALT  PAVEMENTS 


Sieve  Numbers 

FOR  HEAVY  TRAFFIC 

FOR  LIGHT  TRAFFIC 

Design  1 

Limiting 
Values  2 

Design  » 

Limiting 
Values  2 

Passing  10-mesh  and  retained  on  20-mesh,  %. 
20-mesh  and  retained  on  30-mesh, 
30-mesh  and  retained  on  40-mesh, 
Total  coarse  sand  

5 
8 
10 
23 

2-  8 
5-10 
10-15 
17-30 

10 
10 
15 
35 

5-12 
10-15 
10-20 
25-40 

Passing  40-mesh  and  retained  on  50-mesh, 
50-mesh  and  retained  on  80-mesh, 
Total  medium  sand  

Passing  80-mesh  and  retained  on  100-mesh, 
100-mesh  and  retained  on  200-mesh, 
Total  fine  sand  

Passing  200-mesh  

13 
30 
43 

17 
17 
34 

0 

5-30 

5-40 

15 
30 
45 

10 
10 
20 

0 

10-30 
10-40 

6-15 
10-15 
18-25 

0-  5 

10-20 
10-25 
25-40 

0-  5 

1  Richardson's  "  Asphalt  Construction,"  McGraw-Hill  Book  Co.,  N.  Y. 
allows  a  variation  of  ±5  from  standard  values. 

2  Blanchard's  "Highway  Engineers'  Handbook,"  Wiley  &  Sons,  N.  Y. 


Richardson 


considered  better  but  the  cost  is  greater.  Other  stone  dusts, 
marl,  clay,  etc.,  have  been  used  with  success.  Since  only  the 
impalpable  powder  can  enter  the  voids  of  the  fine  sand  grains 
the  stone-dust  should  be  ground  so  that  at  least  two-thirds  will 
pass  a  200-mesh  sieve.  That  failing  to  pass  acts  as  so  much  sand 
and  should  be  taken  into  account  in  the  design  of  the  mixture. 
Some  native  asphalts,  such  as  Trinidad,  contain  a  considerable 
proportion  of  mineral  matter  which  authorities  agree  may  be 
considered  as  part  of  the  necessary  filler. 

Complete  Topping  Mixture  Design. — Richardson 1  con- 
siders the  points  to  be  especially  regraded  in  designing  the 
wearing  course  of  an  asphalt  pavement  to  be:  1st,  The  Fine 
Sand;  2d,  The  Coarse  Sand;  3d,  The  Filler;  and  4th,  The 
Bitumen.  From  his  experience  he  gives  the  following  as  a 
"  correct  surface  mixture  "  for  heavy  traffic: 


Modern  Asphalt  Pavement." 


TOPPING   MIXTURE 


319 


ASPHALT  SURFACE  MIXTURE 


Bitumen, 
10.5% 
(4th  point) 


Correct 

Filler  + 

Surface 

Mineral  aggre- 

200-mesh sand 

Mixture 

gate  85.9% 

13.0% 

100% 

(1st  point) 

(3d  point) 

Mesh 

(2d  point) 

100              13.0' 

(3d  point) 

80              13.0, 

(1st  point) 

50 

Sand  76.5% 

40 

'* 

(1st  point) 

(2d  point) 

30                8.0 

20                5.0 

10                3.0 

(2d  point) 

26.0% 

23.5% 
11.0% 

16.0% 


Construction. — The  wearing  course- mixture  (topping)  is  pre- 
pared in  a  plant  similar  to  that  used  for  bituminous  concrete 
(Figs.  165,  166).  The  sand  is  either  fed  into  the  drying  drum 
from  sources  such  that  the  mixture  when  elevated  to  the  bin 
will  be  according  to  the  predetermined  design,  or  it  is  dried 
and  screened  separating  it  into  several  portions  in  order  that  it 
may  be  remixed  in  proper  proportions.  The  sand  after  heating 
is  stored  in  a  hopper  bin  above  the  measuring  or  weighing 
device  into  which  it  may  be  drawn  by  gravity  and  dropped  into 
the  mixer.  Carefully  measured  hot  asphalt  cement  and  stone- 
dust,  usually  cold,  are  put  in  the  mixer  with  the  sand  and  the 
whole  turned  until  uniformly  mixed.  It  is  then  transported 
to  the  roadway  in  wagons.  The  mixture  leaves  the  plant  at  a 
temperature  not  exceeding  177°  C.  (350°  F.)  and  reaches  the 
roadway  at  a  temperature  not  less  than  110°  C.  (230°  F.), 
preferably  about  150°  C.  (302°  F.).  The  wagons  are  dumped 
on  the  binder  course  just  ahead  of  the  work  or  on  platforms. 
The  mixture  is  shoveled  to  place  and  raked  smooth  by  hot  iron 
rakes,  after  which  it  is  rolled  and  tamped  until  satisfactorily 


320  BITUMINOUS   ROADS 

compressed.  A  small  tandem  roller  (about  8  tons)  is  first  used 
then  a  heavy  one  (about  12  tons).  Hot  tampers  are  used  along 
the  edges  or  in  places  inaccessible  to  the  rollers. 

Maintenance. — The  ordinary  maintenance  consists  in  repair- 
ing pot  holes  and  other  defects  that  may  appear  due  to  wear, 
excessive  pressure  by  vehicles,  rotting  under  the  influence  of 
dampness  from  beneath  or  on  top,  openings  for  pipes  or  under- 
ground work,  or  imperfect  design  and  construction.  Even  if 
the  wear  is  uniform  there  will  come  a  time  when  the  whole  top 
will  have  to  be  replaced.  When  defects  occur  two  methods  of 
procedure  are  available.  In  one  the  surface  is  heated  by  hot 
pans  drawn  over  it  or  by  flames  projected  against  it  and  the 
surface  thus  softened  scraped^  away  f  to  1  inch  in  depth  and 
replaced  by  new  topping.  In  the  other  method  the  wearing 
and  binder  courses  are  cut  through  vertically  making  a  rect- 
angular opening  to  the  foundation  and  this  filled  with  new 
binder  and  topping,  and  tamped  or  rolled  to  place.  The  edges, 
especially  in  old  pavements,  should  be  uniformly  painted  with 
a  thin  coating  of  asphalt  cement  to  insure  the  adherence  of  the 
new  and  old  work.  Cracks  are  usually  widened  and  new 
material  tamped  in.  Tar  or  asphalt  cement  may  be  used  to 
fill  them  but  as  these  have  a  tendency  to  soften  the  surrounding 
surface  they  may  do  more  harm  than  good.  If  the  design  of 
the  pavement  is  suitable  to  the  traffic,  small  cracks  will  be 
closed  automatically  by  the  pounding  and  kneading  of  hoofs 
and  vehicles. 

Rock  Asphalt. — Sandstone  or  limestone  naturally  impreg- 
nated with  asphalt  is  known  as  rock  asphalt.  This  stone  is 
quarried  and  broken  into  fragments  and  used  as  macadam,  or, 
it  is  pulverized,  heated  and  spread  like  sheet  asphalt.  The 
principal  objection  to  its  use  is  lack  of  uniformity  in  the  bitu- 
men content,  which  varies  from  3  to  10  per  cent,  with  no 
assurance  that  contiguous  parts  of  the  roadway  will  be  any- 
where near  the  same.  If  some  easy  method  could  be  devised 
to  mix  the  broken  or  pulverized  rock  in  large  quantities  and 
so  thoroughly  that  it  would  have  a  uniform  bitumen  con- 
tent, increased  by  adding  asphalt  cement  if  necessary,  rock 


ASPHALT   BLOCKS  321 

asphalt,  would  no  doubt  prove  highly  successful  for  roads  near 
the  quarries  where  freight  charges  would  not  be  a  barring 
factor. 

Asphalt  Blocks. — Blocks  about  12  inches  long,  5  inches  wide, 
and  2,  2^  of  3  inches  deep  made  up  of  a  mixture  approaching 
in  composition  the  Topeka  formula  (p.  309),  are  molded  hot 
in  the  factory  under  a  pressure  of  30,000  to  50,000  pounds  per 
square  inch.  These  are  then  transported,  after  cooling,  to  the 
roadway  and  laid  on  a  concrete  or  other  firm  foundation  in  a 
similar  manner  to  brick  or  stone  blocks.  They  are  laid  as 
closely  together  as  possible  and  no  allowance  need  be  made  for 
expansion.  A  thin  layer  of  sand  over  the  newly  laid  blocks  will 
fill  the  joints. 


CHAPTER  XIV 

SURFACE  TREATMENTS  TO  MITIGATE  AND 
PREVENT  DUST 

IT  has  already  been  stated  that  impalpably  fine  dust  (clay 
and  rock  powder)  is  the  cement  which  finally  binds  broken  stone 
road  metal  into  a  comparatively  monolithic  mass.  The  same 
is  true  of  gravel  and  in  a  much  less  degree  of  sand-clay  and 
earth.  The  cementing  of  stone  and  gravel  is  probably  due  to 
chemical  action  while  the  stability  of  earth  and  sand-clay  may 
depend  almost  wholly  upon  the  physical  properties  of  cohesion, 
friction,  and  the  surface  tension  or  adhesion  of  the  moistening 
water  for  the  earth  particles.  All  of  these  properties  seem  to 
function  better  in  the  presence  of  moisture;  therefore  when  the 
water  is  dried  out  the  roadway  under  the  action  of  traffic  soon 
begins  to  disintegrate  and  becomes  dusty.  Dust  is  defined  by 
the  Century  Dictionary  as  "  earth  or  other  matter  in  fine  dry 
particles  so  attenuated  that  they  can  be  raised  and  carried  by 
the  wind."  The  roadway  is  the  most  fertile  source  of  dust,  and 
dust,  being  a  carrier  of  disease  germs  and  an  irritant  of  delicate 
tissues,  is  well  known  to  be  a  menace  to  the  health  of  man, 
horses,  cattle,  and  other  animals,  besides  being  very  uncom- 
Ortable.  Also,  when  it  settles  upon  the  leaves  of  plants 
it  gives  them  a  bad  appearance  and  hinders  their  growth  by 
interfering  with  their  natural  functions. 

Road  dust,  while  instrumental  in  preserving  a  roadway,  is 
seen  to  be  at  the  same  time  a  nuisance.  The  problem  then  is  so 
to  treat  the  road  surface  that  the  dust  nuisance  may  be  mit- 
igated or  prevented  and  the  bond  of  the  roadway  at  the  same 
time  retained  or  bettered. 

Cause  of  Dust. — Hubbard,  after  stating  the  cause*  of  dust  to 

322 


DUST  AND   ITS  EFFECT  323 

be  wear,  classifies  the  dust-making  agencies  under  three  heads: 1 
chemical,  physical,  and  mechanical.  Water  and  weak  acids 
carried  in  water  act  upon  rocks  to  decompose  their  mineral 
constituents  and  break  them  down,  chemically,  into  fine  par- 
ticles.2 The  disrupting  effect  of  frost,  the  attrition  of  falling 
rain,  the  transporting  power  of  water  and  the  action  of  wind 
comprise  the  physical  agencies;  while  the  mechanical  are 
abrasion,  impact,  local  compression,  and  shear.  To  combat 
the  dust  nuisance  it  will  be  necessary  either  to  prevent  the 
formation  of  dust,  to  treat  the  roadway  with  something  which 
will  retain  the  dust  on  the  surface,  or  to  remove  it  by  some 
mechanical  means  such  as  sweeping 'and  washing.  The  last 
method  is  employed  for  pavements  in  oities  but  is  not  prac- 
tical for  the  ordinary  rural  roads. 

Earth  is  an  unstable  material  when  very  wet  and  an  extremely 
friable  one  when  very  dry,  but  forms  a  comfortable  and  reason- 
ably good  road  surface  for  light  traffic  when  in  just  the  right 
condition  of  moisture.  Hence  the  logical  maintenance  of  an 
earth  road  is  to  crown  and  smooth  it  so  that  excessive  water 
will  readily  run  off;  at  the  same  time  the  work  on  the  surface 
should  be  such  as  to  cause  it  to  become  so  dense  that  it  takes  up 
the  water  slowly  and  dries  out  slowly,  thus  retaining  for  a  con- 
siderable time  the  necessary  moisture  to  hold  it  together. 

The  same  statement  may  be  made  of  sand-clay  roads  for, 
indeed,  ordinary  earth  or  loam  is  a  mixture  of  sand  and  clay 
but  probably  not  in  the  best  proportion  for  road  surfaces. 

When  there  is  intermixed  such  a  proportion  of  pebbles  that 
the  road  may  be  considered  a  gravel  road,  strength  and  power 
to  resist  wear  is  given  by  both  the  chemical  binding  action 
and  the  mechanical  stability  due  to  the  coarser  materials.  But 
here  again  too  great  an  amount  of  water  and  too  little  water 
are  both  detrimental.  The  ideal  road  can  only  be  maintained 

1  "Dust  Preventives  and  Road  Binders,"  by  Prevost  Hubbard,  Wiley 
&  Sons,  New  York. 

2  See  U.  S.  Department  of  Agriculture,  Bureau  of  Chemistry  Bulletins, 
85,  92,  and  28,  by  Page,  Cushman  and  Hubbard,  on  the  "Cementing  Power 
of  Road  Materials,"  "The  Effect  of  Water  on  Rock  Powders,"  and  "The 
Decomposition  of  Feldspars." 


324         SURFACE    TREATMENT    TO    PREVENT    DUST 

with  a  mean  between  these  extremes  or  by  an  artificial  bonding 
cement. 

With  a  water-bound  broken  stone  road  similar  conditions 
apply,  but  the  stone  being  angular  there  is  still  greater  stability 
an<J  when  wedged  firmly  together  by  the  roller  will  withstand 
well  the  mechanical  disrupting  factors,  while  the  moist  disin- 
tegrating rock  powder  settling  between  the  stones  serves  further 
to  cement  thgm  together  into  a  more  or  less  monolithic  mass. 
Excessive  water  in  addition  to  softening  the  subgrade  washes 
away  the  "  fines  ";  with  insufficient  moisture,  though  there  may 
be  plenty  of  dust,  cementation  and  recementation  cannot  take 
place. 

With  still  more  stable  roadways  an  artificial  cement  takes 
the  place  of  the  natural  "  dust  cement/'  as  in  concrete  and 
bituminous  pavements;  or,  definitely  shaped  blocks — brick, 
stone,  wood,  etc.,  are  carefully  laid  so  as  to  resist,  quite  effect- 
ually, the  destructive  action  of  traffic. 

But  roadways  can  not  always  be  in  ideally  moist  condition. 
And  even  if  they  could  be  and  no  wear  at  all  took  place,  dirt 
would  be  tracked,  blown  and  washed  upon  them  from  outside. 
Twigs  and  leaves  from  trees,  droppings  from  animals,  soot  from 
chimneys,  debris  from  mills,  and  many  other  things  furnish 
material  for  street  litter.  This  litter  is  ground  up  into  dust 
which  when  raised  by  the  wind  becomes  a  nuisance.  If  this 
dust  would  remain  on  the  surface,  even  though  it  had  no  bind- 
ing power,  and  mnch  of  it  has  not,  it  would  serve  as  a  cushion 
to  prevent  further  wear.  But,  under  the  action  of  traffic  and 
wind  the  road  may  be  depleted  of  its  dust,  which,  while  decreas- 
ing the  dust  nuisance,  leaves  the  roadway  without  its  natural 
protective  and  repair  agency,  and  hence  subject  to  continued 
and  more  harsh  and  violent  usage. 

PALLIATIVES  AND  PREVENTIVES 

Those  substances  which  when  applied  to  the  roadway  tem- 
porarily lay  dust  are  technically  known  as  palliatives;  those 
whose  effect  is  more  permanent,  good  for  six  months  to  two  years, 
are  called  preventives. 


PALLIATIVES  325 

Palliatives.  Water. — The  use  of  water  as  a  dust  layer  is 
universal,  and  when  properly  applied  is  effective.  The  prin- 
cipal objections  to  its  use  are  its  temporary  nature  and  that  the 
roadway  immediately  after  application  is  muddy  and  slippery. 
The'  usual  method  of  applying  water  is  by  means  of  horse- 
drawn  sprinkling  carts.  These  are  tanks  mounted  upon  wagons 
having  suitable  valves  and  orifices  for  spreading  the  water.  It 
has  been  pretty  well  demonstrated  that  efficient  sprinkling  will 
materially  prolong  the  life  of  a  road  under  horse-drawn  iron- 
tired  traffic,  but  it  will  not  prevent  damage  by  rapidly  moving 
motor  cars. 

The  cost  of  water  sprinkling  will  depend  on  the  character 
of  the  road,  the  climate,  the  cost  and  efficiency  of  labor,  and 
the  cost  and  availability  of  water.  Country  roads  could  hardly 
be  treated  continuously  with  water. 

Sea  water,  because  it  contains  some  hygroscopic  mag- 
nesium salts,  can  in  some  places  be  used  with  success.  Objec- 
tion has  been  raised  to  the  residue  of  white  salt  scale  that  ap- 
pears when  the  water  dries  out.  Except  when  the  water  is 
easy  to  obtain  it  will  not  pay  to  use  it. 

Oil  and  water,  mechanically  mixed  in  a  tank  by  whirling 
blades  then  immediately  forced  upon  the  roadway,  has  been 
used  to  some  extent.  The  theory  being  that  when  the  water 
evaporates  a  very  thin  film  of  oil  will  be  left. 

Deliquescent  salts  such  as  common  table  salt  (a  mixture  of 
sodium  chloride  and  magnesium  chloride)  and  calcium  chloride 
have  also  been  used  somewhat.  These  may  be  spread  dry  or 
dissolved  in  water  and  sprinkled  from  a  water  wagon.  Being 
hygroscopical  they  will  attract  moisture  from  the  air  and  keep 
the  road  from  drying  out  for  a  considerable  time,  depending 
on  the  character  of  the  road  and  the  climate  and  weather  con- 
ditions. About  1  to  \\  pounds  to  the  square  yard  is  recom- 
mended for  a  first  application  of  calcium  chloride  in  its  dry  state 
upon  a  macadam  or  gravel  road.  A  farm  lime  spreader  may 
be  used  advantageously  for  distributing.  This  treatment  is 
followed  in  periods  of  one  or  two  months  by  applications  one- 
half  as  great.  In  very  dry  weather  it  may  be  necessary  to 


326        SURFACE    TREATMENT   TO    PREVENT    DUST 

sprinkle  with  water  occasionally.  The  wet  method  which  is 
recommended  for  hard  surfaced  roadways  consists  in  dis- 
solving salt  in  water  and  sprinkling  it  on  the  surface.  One 
pound  of  salt  to  a  gallon  of  water  is  recommended.  Subse- 
quent applications  to  be  made  every  three  or  four  weeks,  depend- 
ing on  the  weather. 

Emulsions. — Water  and  soap  or  other  saponifying  agents 
such  as  potash,  ammonia,  soda,  or  carbolic  acid,  are  mixed 
with  mineral  oil,  or  tar  agitated  until  emulsified,  and  sprin- 
kled upon  the  road.  Good  results  cannot  be  obtained  with 
paraffin  oils.  They  are  too  greasy  and  non-adhesive.  With 
asphaltic  oils  repeated  applications  may  produce  a  carpet  or 
mat  of  appreciable  thickness  which  acts  both  as  a  dust  layer 
and  as  a  road  protector.  Emulsions  may  be  purchased  or  made 
up  in  concentrated  form,  shipped  or  hauled  to  the  place  of  use, 
there  diluted  with  water  to  secure  the  desired  strength  and 
applied.  A  Boston  method  is  to  dissolve  25  to  30  pounds  of 
cottonseed  soap  in  100  gallons  of  hot  water;  to  this  solution  is 
added  200  gallons  of  emulsion  oil  and  the  mixture  agitated  for 
twenty  minutes.  This  forms  a  concentrated  solution.  It  is 
reduced  about  one  of  solution  to  four  of  water  for  first  applica- 
tion and  about  one  to  eight  for  subsequent  applications.  One 
gallon  of  the  diluted  mixture  will  cover  about  6  square  yards  of 
surface.  In  a  week  or  ten  days  after  the  first  application  a 
second  application  should  be  made.  Succeeding  applications 
will  be  required  at  periods  of  two  to  six  weeks,  depending  on 
the  type  of  roadway,  weather  and  climatic  conditions. 

Organic  substances  such  as  waste  from  sugar  factories 
and  paper  mills  are  used  as  palliatives.  These  products  being 
more  or  less  sticky  form  with  the  dust  a  thin  mat. 

Sugar  Waste. — A  poor  grade  of  molasses  diluted  with  water 
to  make  it  thin  enough  to  run  from  the  sprinkler  and  reduce  its 
stickiness  so  that  it  will  not  adhere  to  the  wagon  wheels  has 
been  found  helpful  to  the  roads  near  sugar  factories.  How- 
ever, the  loads  of  beets  and  sugar  cane  are  so  heavy  that  they 
soon  cut  up  any  road  but  the  very  best. 

Paper  Mill  Waste. — Waste  sulphite  liquor  from  the  man- 


PALLIATIVES 


327 


ufacture  of  wood  pulp  has  been  used  to  a  considerable  extent. 
The  dispensers  of  a  preparation  of  this  character,  under  the 
trade  name  of  Glutrin,  claim  that  it  acts  upon  the  silica  of  the 
stone-dissolving  it  and  forming  a  bond  insoluble  in  water. 
The  liquor  is  shipped  to  the  place  of  use  in  concentrated  form, 
there  mixed  with  water  and  sprinkled  on  the  surface. 

Light  Oils. — Crude  petroleum  and  petroleum  distillates  are 


FIG.  168.— Oil  Distributor. 

largely  used  as  dust  palliatives.  Only  those  oils  having'  an 
asphalt  base  (35  per  cent  or  more  asphalt)  are  considered  of  real 
value  for  this  purpose.  Non-asphaltic  oils  are  temporary  in 
their  effect  but  not  being  sticky  do  not  require  covering  with 
sand.  The  residual  oils  from  the  petroleum  refineries  have 
been  most  successful  in  California  where  "the  long  dry  season 
makes  the  main  traveled  untreated  earth  roads  extremely 
dusty  and  uncomfortable. 


328         SURFACE    TREATMENT    TO    PREVENT    DUST 

Earth  roads  will  require  three  or  four  treatments  to  keep 
them  in  the  best  condition.  They  are  first  properly  shaped  with 
the  road  machine  and  the  light  oil  sprinkled  on  the  surface  to 
the  amount  of  about  \  gallon  per  square  yard.  Subsequent 
applications,  if  made  before  the  roadway  has  become  rutted 
or  out  of  shape,  will  require  about  half  that  amount  of  oil.  It 
is  recommended  that  the  road  be  sprinkled  with  water,  if  very 
dry,  before  application.  After  a  light  rain  is  a  good  time  to 
apply  the  oil. 

Macadamized  and  other  hard-surfaced  roadways  should  first 
be  swept  clean ;  dry,  if  that  removes  the  dirt,  if  it  does  not  then 
wet  followed  by  another  sweeping  after  it  has  dried.  The  oil  is^ 
applied  at  the  rate  of  \  to  J  gallon  per  square  yard  and  after 
two  or  three  hours  covered  lightly  with  sand  or  dry  earth. 
Gravity  or  pressure  distributors,  Fig.  168,  are  more  efficacious 
than  hand-pouring  cans,  although  the  latter  are  useful  for  small 
jobs  and  for  patching. 

Heavy  residual  oils  are  frequently  cut  back  by  a  flux  and 
applied  in  the  same  manner  as  the  light  oils.  The  flux  soon 
evaporates,  leaving  the  heavier  asphalt  thinly  but  uniformly 
spread  over  the  surface. 

Tars. — Light  tars  of  various  kinds  are  used  in  the  same 
manner  as  oils.  Pressure  distributors  are  recommended  as 
spreading  the  tar  most  evenly.  Light  tars  are  usually  applied 
cold  in  warm  weather  but  may  be  heated  if  too  viscous  to  flow 
well.  Crude  and  refined  tars  are  used;  refined  tars  are  con- 
sidered better  but  are  of  such  a  consistency  that  they  have  to 
be  heated.  It  may  pay,  however,  to  use  the  refined  and  heavier 
tars,  as  the  number  of  applications  per  season  will  be  reduced. 
From  five  to  ten  hours  is  allowed  to  elapse  before  covering  the 
tarred  surface  with  stone  screenings  or  sand. 

Animal  and  Vegetable  Oils. — These  are  sometimes  mixed 
with  an  alkali  to  form  a  soap  which  can  be  used  later  to  make 
an  emulsion  with  a  mineral  oil.  If  used  alone  they  are  short 
lived  and  act  as  a  dust  layer  similar  to,  though  more  lasting 
than,  water. 


OILED  ROADS  329 


PREVENTIVES,  BITUMINOUS  SURFACES 

The  so-called  preventives  are  practically  all  made  up  of 
mixtures  or  compounds  containing  bitumen  as  its  binding  ingre- 
dient. Oils  and  tars  when  applied  frequently  may  produce 
surfacings  of  appreciable  thickness  which  have  sufficient  per- 
manency to  be  called  preventives.  The  point  where  palliatives 
disappear  and  preventives  begin  cannot  be  definitely  defined. 
Bituminous  surfaces  are  road  preservatives  as  well  as  dust 
preventives;  in  fact,  that  may  and  often  is  their  primary  sig- 
nificance. They  are  classified  either  according  to  the  materials 
used,  as,  oil,  tar,  asphalt;  or  according  to  their  thickness — a 
coating,  if  less  than  J-inch  thick  and  a  carpet  or  blanket  if  more. 

Materials. — The  most  satisfactory  materials  for  these  sur- 
faces are:  (a)  petroleum  residual  oils  having  an  asphaltic 
base,  (6)  cut-back  asphalts,  (c)  refined  coal  tars,  ,(cf)  refined 
water-gas  tars,  (e)  cut-back  coal  tar  pitches,  and  (/)  com- 
binations of  tars  and  asphalts.  The  residual  oils  are  ordi- 
narily used  on  earth  roads;  tars  and  cut-back  asphalts  and 
pitches  on  gravel,  broken  stone  or  paved  surfaces.  Which  is 
better,  the  tars  or  petroleum  products,  is  a  disputed  question. 
And  while  the  heavy  materials  carry  more  bitumen,  build  up 
mats  quicker  and  last  longer,  they  should  not  be  too  viscous 
for  ready  application. 

Specifications. — Since  these  will  depend  upon  local  con- 
ditions as  well  as  the  materials  used,  and  are  highly  technical 
in  character  detailed  specifications  are  omitted.  Specimen 
specifications  may  be  obtained  from  most  of  the  state  highway 
departments  or  from  the  Office  of  Public  Roads,  United  States 
Department  of  Agriculture.  The  table  on  page  330  gives  the 
characteristics  required  by  typical  specifications. 

Oiled  Roads. — The  desire  to  eliminate  the  dust  nuisance  at 
a  cost  less  than  sprinkling  with  water  led,  in  California,  to  the 
use  of  heavy  residual  petroleum  oil.  The  asphaltic  base  of  the 
oil  cemented  the  particles  of  earth  and  sand  together,  making  a 
rubbery  coating  over  the  road  surface.  This  proved  to  be  so 
much  better  than  the  original  earth  surface,  in  dry  weather 


330         SURFACE    TREATMENT    TO    PREVENT    DUST 


11 


«    o> 


1       1C        1          1 

'(MOO 
0.^0000 


111+ 


o.        ^ 

co        ^ 


:  + 


•  Tti 

•  O 
-CO 


00  g  a 


I  £ 


i  + 
3  u 


o 


»o    ? 

3 


O 


OILED    ROADS 


331 


eliminating  the  dust  and  in  wet  weather  the  mud,  that  many 
miles  of  road  were  systematically  oiled.  While  a  very  great 
improvement,  they  are  not  sufficiently  durable  under  moder- 
ately heavy  traffic  to  commend  their  general  use  for  country 
roads.  They  are  being  replaced  as  circumstances  demand  by 
more  durable  types.  But  just  as  earth  roads  will  always  be 
with  us,  and  under  favorable  circumstances  are  the  cheapest 
and  best  road  for  certain  localities,  so  there  will  be  need  for  the 
oiled  road. 

Construction. — The  road  surface  is  plowed  up  to  a  depth  of 


FIG.  169.— Sheep's  Foot  Roller. 

aboat  6  inches  and  thoroughly  pulverized  with  disk  and  tooth 
harrows.  Oil,  with  an  asphaltic  base,  is  distributed  over  the 
surface  to  the  amount  of  about  1  gallon  per  square  yard.  This 
is  allowed  to  stand  for  a  short  time  to  soak  in  when  the  road  is 
brought  to  the  proper  crown  with  a  road  machine.  It  may  be 
necessary  to  sprinkle  on  a  little  dry  soil  from  the  side  where  the 
oil  remains  sticky.  The  roadway  is  then  rolled  thoroughly. 
When  a  sheep's  foot  or  tamping  roller,  Fig.  169,  is  used,  the 
impregnated  soil  is  rolled  until  the  tampers  on  the  roller  which, 
at  the  beginning  sink  in  full  depth,  fail  to  penetrate  the  sur- 


332         SURFACE    TREATMENT    TO    PREVENT    DUST 

face  materially.  The  roadway  is  then  smoothed  up  with  the 
road  machine  and  rolled  with  a  heavy  roller.  Roads  built  in 
this  manner  have  proved  to  be  quite  satisfactory.  A  surface 
treatment  of  screened  gravel  and  asphaltic  oil  is  sometimes 
given  the  wearing  surface. 

Oil. — In  all  petroleum-oiled  roads  it  is  quite  essential  that 
the  oil  used  has  an  asphaltic  base.  Residual  oil,  that  is,  that 
remaining  after  the  lighter  oils,  naphtha,  benzine,  gasoline, 
kerosene,  and  lubricants  have  been  driven  off  is  considered 
best  as  the  percentage  of  asphalt,  which  constitutes  the  binding 
power,  is  then  greatest.  Care  must  be  observed  that  the  oil 
has  not  been  heated  to  that  point  which  will  destroy  the  tenacity, 
ductility  and  adhesiveness  of  the  asphalt, 


CHAPTER  XV 
REVENUE,     ADMINISTRATION     AND     ORGANIZATION 

Revenue. — The  revenues  for  the  construction  and  mainte- 
nance of  roads  are  usually  derived  from  taxes.  A  few  roads 
have  been  built  by  private  corporations  and  operated  by  exact- 
ing tolls.  The  tendency  is  for  these  to  be  taken  over  by  the 
public  and  made  free  highways.  New  additions  to  cities  often 
have  the  streets  graded  and  paved,  as  a  promotion  proposition 
before  the  plats  are  filed  for  record.  Occasionally,  a  wealthy 
man  or  firm  builds  a  road  and  gives  it  to  the  public.  The  most 
notable  example  is  the  Dupont  road  in  Delaware.  No  better 
way  for  erecting  a  lasting  memorial  can  be  imagined  than  the 
endowment  of  a  fund  for  constructing  and  maintaining  a  well- 
traveled  road.  Of  late  years  there  is  a  growing  tendency  to 
license  automobiles  and  devote  the  revenue  derived  therefrom 
for  the  use  of  highway  improvement  or  for  the  maintenance  of  a 
State  highway  department. 

Taxes,  Direct. — Direct  taxes  are  levied  upon  persons  and 
property.  When  levied  upon  persons  they  are  called  poll  or 
capitation  taxes.  Poll  taxes  are  usually  levied  upon  persons 
of  a  prescribed  class:  For  example,  "  all  able-bodied  males 
between  the  ages  of  21  and  50  inclusive,"  or  "  all  voters  under 
55  years  of  age."  Taxes  are  levied  upon  property  (1)  in  propor- 
tion to  its  value  or  (2)  because  of  nearness,  or  other  reasons,  it 
is  especially  benefited  by  the  improvements.  The  former  is 
usually  known  as  a  property  tax  and  the  latter  as  a  special  tax. 
In  most  States  the  laws  require  property  taxes  to  be  levied 
uniformly  over  the  entire  taxed  district  which  usually  coin- 
cides with  some  civil  district  such  as  city,  township  or  State. 

Special  taxes,  on  the  contrary,  are  not  levied  uniformly 
over  the  taxed  district.  They  are  levied  to  defray  the  cost  of  a 

333 


334     REVENUE,   ADMINISTRATION   AND   ORGANIZATION 

special  improvement  and  can  be  used  for  nothing  else.  The 
improvement  must  be  demanded  by  public  interest  and  the 
taxes  are  levied  upon  property  especially  benefited  and  in  direct 
proportion  to  the  benefits  accruing  to  the  property.  Ordinary 
property  taxes  are  levied  hi  proportion  to  the  value  of  the 
property,  that  is,  presumably,  according  to  the  ability  of  the 
owner  to  pay,  and  not  in  proportion  to  special  benefits  derived 
from  taxation. 

Labor  taxes  are  direct  taxes  which  are  to  be  paid  in  labor. 
They  may  be  either  poll  or  property  taxes.  Road  taxes  from 
the  earliest  levying  of  such  to  within  very  recent  times  have 
been  largely  labor  taxes.  But  as  lines  of  work  become  more 
specialized  the  tendency  is  to  do  away  with  labor  taxes  alto- 
gether, to  pay  the  taxes  in  cash  and  employ  men  versed  in  road- 
making  and  maintenance  to  care  for  the  public  highways. 

General  taxes  are  often  levied  over  a  county  or  State  for 
the  use  of  the  roads  of  the  county  or  State  as  a  whole.  The 
funds  arising  are  not  expended  uniformly  upon  all  the  roads  but 
at  such  places  as  the  proper  officers  may  direct.  They  may 
also  be  used  for  county  or  State  aid,  of  which  more  will  be  said 
under  the  head  of  Administration. 

Indirect  Taxation. — Where  money  is  derived  from  national 
aid  for  road  purposes  it  comes  from  indirect  taxation.  State 
aid,  if  the  State  taxes  be  collected  in  one  general  fund,  may 
likewise  be  classed  as  indirect  taxation,  although  the  State  tax 
is  itself  a  direct  tax.  Another  form  of  indirect  tax  comes  from 
the  employment  of  convicts  for  road  building,  the  convicts 
themselves  being  cared  for  from  a  fund  for  that  purpose  and 
not  specially  raised  for  road  work. 

Bonds. — Bonding  a  district  is  a  method  of  borrowing  money 
and  spreading  the  payment  over  a  series  of  years  in  order  that 
the  levy  of  any  one  year  shall  not  be  excessive.  This  method 
of  financing  road  projects  has  been  quite  popular.  The  total 
of  such  bonds  according  to  the  U.  S.  Office  of  Public  Roads  up 
to  January  1,  1914,  was  $286,557,073.1  The  amount  of  out- 
bulletin,  136,  U.  S.  Dept.  of  Agriculture,  "Highway  Bonds,"  by 
Hewes  and  Glover. 


REVENUE,   TAXES  335 

standing  local  highway  bonds  January  1,  1913,  was  approx- 
imately $202,007,776.  The  grand  total  of  all  highway  bonds 
State,  county,  township,  municipal  and  district,  reported  to  the 
Office  of  Public  Roads,  to  January  1,  1914,  was  $445,147,073. 

Kinds  of  Bonds.  —  Bonds  may  be  classified  according  to  the 
manner  of  payment  as  sinking-fund,  serial  and  annuity. 

Sinking-fund.  —  These  are  straight  terminal  bonds,  the 
interest  being  paid  annually  upon  the  principal,  which  is  the 
face  value  of  the  issue,  or  at  some  other  fixed  regular  period. 
In  order  to  pay  the  bonds,  a  sinking-fund  is  established.  There 
is  theoretically  paid  into  this  sinking-fund  annually  a  certain 
sum.  The  sinking-fund  is  then  loaned.  The  payments  and 
interest  are  together  such  that  they  will  amount  to  the  face  of 
the  bond  at  its  maturity.  The  interest  which  the  sinking-fund 
draws  may  not  be  as  large  as  that  of  the  bond.  Even  though 
the  nominal  interest  rate  is  the  same,  there  is  always  time  lost 
between  the  collection  of  the  tax  and  its  investment.  For  this 
reason  and  from  the  fact  that  a  sinking-fund  may  be  easily 
drawn  upon  for  other  purposes  than  that  for  which  it  was 
created  makes  this  the  least  desirable  class  of  bonds. 

The  sinking-fund  which  must  be  raised  to  amount  to  P 
dollars  in  n  payments  at  an  interest  rate  of  i  per  cent  may  be 
obtained  by  the  formula- 

Sinking-fund  = 


EXAMPLE 

What  sinking-fund  must  be  raised  to  discharge  a  debt  of  $10,000  in 
five  years  at  4  per  cent  annual  interest? 
Solution  : 


»10-000 


Log  1.046  =  51og  1.04 

=  5X0.017033 
=  0.085165 
1.046  =  1.2166 
(1  +  .04)6-  1=0.2166 


336     REVENUE,   ADMINISTRATION   AND   ORGANIZATION 


log  S  =  log  .04+log  10,000-log  0.2166 

=  (8.602060  - 10)  +4.0  -  (9.335658  - 10) 
=  3.266402 
S  =  $1846.27. 

Interest,  annuity,  and  sinking-fund  tables  are  published 
and  may  be  seen  at  almost  any  bank  or  money  brokers'. 
The  sinking-fund  table  gives  the  value  of  the  fractional  coeffi- 
cient in  the  formula,  or  the  sinking-fund  which  will  amount  to 
1  in  n  years.  Such  a  table  is  printed  in  Bulletin  136,  U.  S. 
Department  of  Agriculture.  Here  in  the  column  marked  4  per 
cent  and  the  limit  five  years,  is  found  0.1846271;  this  multi- 
plied by  $10,000  gives  the  same  result  as  obtained  above. 

The  following  tabular  statement  shows  the  growth  of  the 
fund: 

TABLE  I 


Year 

Sinking-fund 
at  Beginning  of 
Year 

Interest  during 
Year 

Annual  Pay- 
ment into 
Sinking-fund 

Total  S.  F. 
End  of  Year 

1 

0 

0 

$1,846.27 

$1,846.27 

2 

$1,846.27 

$73.85 

1,846.27 

3,766.39 

3 

3,766.39 

150.66 

1,846.27 

5,763.32 

4 

5,763.32 

230.53' 

1,846.27 

7,840.12 

5 

7,840.12 

313.61 

1,846.27 

10,000.00 

Totals 

$768  65 

$9,231  35 

If  this  loan  bore  4J  per  cent  interest  the  cost  to  the  borrower 
would  have  been  $10,000  principal +$2250  interest  less  $768.65 
interest  on  sinking-fund  =$11,481.35;  or,  Interest  on  loan 
$2250+ Sinking-fund  payments  ($1846.27X5)  =$11,481.35. 

Serial  Bonds. — The  serial  method  retires  a  fixed  annual 
amount  of  the  principal  each  year.  Usually  the  amount  so 
retired  is  an  aliquot  part  of  the  whole.  The  annual  payment, 
therefore,  is  the  fixed  payment  of  principal  plus  the  interest  on 
the  unpaid  principal. 


SINKING-FUND.     SERIAL   BONDS 


Here,  if  the  principal  is  P,  the  annual  payment  is  -.-,  the 

interest  for  the  kth  year  is  ( P+  (I- k)- }i  =  Pi(l+^-~—}suid  the 

\  »/  \       >   / 

payment  for  the  same  year  is  Pi- — Ml  H —  "*))•  The  total 
amount  of  interest  paid  up  to  the  end  of  the  kth  year  is 
Pikl  1-f— — —  ) ;  and  the  total  amount  of  interest  and  principal 
paid  up  to  the  end  of  the  kth  year  is 

By  substituting  n  for  k,  the  grand  total  of  interest,  and  interest 
and  principal,  paid  is  readily  found  to  be 

Total  interest  in  n  years      =  - — — —  •     P 


Total  to  discharge  debt 


The  following  table  shows  how  a  $10,000  loan  at  4|  per  cent 
interest  could  be  paid  by  five  serial  payments: 

TABLE  II 


Principle  at 

Interest  for 

Principal  Re- 

Year 

Beginning  of 

Year 

paid  at  End 

Total 

Year 

of  Year 

1 

10,000 

$450 

$2,000 

$2,450 

2 

8,000 

360 

2,000 

2,360 

3 

6,000 

270 

2,000 

2,270 

4 

4,000 

180 

2,000 

2,180 

5 

2,000 

90 

2,000 

2,090 

Totals  

$l;350 

$10,000 

$11,350 

Annuity  bonds  are  those  wherein  a  uniform  periodic  pay- 
ment will  discharge  the  debt  in  a  given  time.     The  necessary 


338     REVENUE,    ADMINISTRATION   AND   ORGANIZATION 


annual  payment  to  discharge  a  debt  P,  interest  rate  i,  in  n 
years  "is  given  by  the  formula 


Annual  payment  = 


EXAMPLE 

Find  the  annual  payment  which  will  discharge  a  debt  of  $10,000  in  five 
equal  payments,  the  rate  of  interest  being  4£  per  cent. 
Solution : 


Log  1.045  =0.019116 
-5  log  1.045  =-0.095580 

=  9.904410-10 

Log"1  (9.904410 -10)  =0.802449 
1-.  802449  =  0.197551 
Log  (Annual  payment)  =log  i— log  0. 197551 +log  P 

=  log  0.045  -log^O.  197551  +log  10,000 
=  (8.653213-10)  -  (9.295679-10)4-4.000000 
=  3.357534 
Annual  payment  =  $2277.916 

The  following  table  shows  the  progress  of  the  repayment 
of  the  loan  of  $10,000  by  annual  payments  of  $2277.92. 

TABLE  III 


Year 

Principal  Owing 
at  Beginning 

Interest  for 

Principal 
Repaid  at 

Total  Pay- 
ment for 

of  Year 

End  of  Year 

Year 

1 

$10,000.00 

$450.00 

$1,827.92 

$2,277.92 

2 

8,172.08 

367.74 

1,910.18 

2,277.92 

3 

6,261.90 

281.79 

1,996.13 

2,277.92 

4 

4,265.77 

191.96 

2,085.96 

2,277.92 

5 

2,179.81 

98.09 

2,179.81 

2,277.90 

Totals  

$1,389.58 

$10,000.00 

$11,389.58 

In  making  up  bonds  it  is  desirable  and  customary  to  have 
them  in  some  number  of  hundreds  and  the  interest  In  dollars 


ANNUITY   BONDS 


339 


only.  This  requires  some  adjustments  from  the  theoretical 
amounts.  Various  adjustments  can  be  made  which  will  keep 
the  annual  payments  near  the  theoretical  amount.  One  for 
the  above  loan  is  shown  in  the  following  schedule: 

TABLE  IV 


Year 

Principal  Owing 
at  Beginning  of 
Year 

Interest  for 
the  Year 

Principal 
Repaid  at  End 
of  Year 

Total  Payment 
for  Year 

1 

$10,000 

$450 

$1,800 

$2,250 

2 

8,200 

369 

2,000 

2,369 

3 

6,200 

279 

2,000 

2,279 

4 

4,200 

189 

2,000 

2,189 

5 

2,200 

99 

2;200 

2,299 

Totals  

$1,386 

$10,000 

$11,386 

Comparison. — The  total  expense  of  a  loan  under  the  sinking- 
fund  plan  is  usually  greatest  and  under  the  serial  plan  least. 
Table  V  shows  the  relative  cost  for  a  $100,000  20-year  loan. 

TABLE  V1 

TOTAL  COST  OF  A  $100,000  LOAN  FOR  20  YEARS  INTEREST  COMPOUNDED 

ANNUALLY 


SINKING-FUND  BOND  COMPOUNDED 

Annual 
Interest  on 

ANNUALLY  AT 

Annuity 
Bond 

Serial 
Bond 

Bonds 

3% 

31% 

4% 

4 

$154,431 

$150,722 

$147,163 

$147,163 

$142,000 

4£ 

164,431 

160,722 

157,163 

153,752 

147,250 

5 

174,431 

170,722 

167,163 

160,485 

152,500 

5* 

184,431 

180,722 

177,163 

167,359 

157,750 

6 

194,431 

190,722 

187,163 

174,369 

163,000 

1  From  Bulletin  136,  U.  S.  Dept.  of  Agriculture. 


340     REVENUE,   ADMINISTRATION  AND  ORGANIZATION 

Licenses. — Licenses  for  the  operation  of  vehicles  may  be 
classed  under  the  heading  of  indirect  taxation.  Many  States 
are  adopting  this  method  of  raising  money  for  road  purposes. 
Illinois  has  recently  (1919)  bonded  the  State  for  $60,000,000  to 
build  trunk  lines  roads  the  whole  of  which  is  to  be  paid  eventu- 
ally from  motor  vehicle  licenses.  In  some  of  the  States  the 
license  fee  is  an  arbitrary  amount  placed  on  all  cars  alike,  in 
others  it  is  based  on  the  rated  horse-power  of  the  car,  and  in 
others  on  the  weight  of  the  loaded  car.  Differentiation  in  fees 
are  usually  made  for  the  several  classifications  of  vehicles  and 
drivers.  Motor-cycles  are  taxed  from  $2  to  $5  per  year;  a 
35-h.p.  pleasure  car  weighing  3000  pounds,  for  example,  from 
$3  to  $35,  with  an  average  of  about  $12;  trucks  and  commercial 
cars,  if  light,  about  the  same  as  pleasure  cars,  while  the  heavier 
ones  go  as  high  as  $250;  chauffeurs  and  owner  operators  are  in 
some  States  also  licensed,  the  fees  being  from  $1  to  $5;  dealers 
in  most  States  are  taxed,  the  license  fee'  ranging  from  $5  to  $50. 

ADMINISTRATION 

Development  of  Road  Systems. — While  roads  have  been 
built  since  the  earliest  history  of  the  world,  it  is  only  within 
comparatively  modern  times  that  systematic  road  systems 
have  been  developed.  Herodotus  speaks  of  an  Egyptian  road 
requiring  100,000  men  a  period  of  ten  years  to  build.  The 
Babylonians,  the  Carthaginians,  the  Chinese,  and  even  the 
Peruvians  built  roads  in  the  dim  vistas  of  the  past,  many  of 
them  magnificent  structures,  but  if  they  developed  any  system- 
atic methods  of  administration,  these  methods  have  been  lost. 

The  great  Roman  roads,  of  which  the  Appian  Way  extend- 
ing from  Rome  to  Capua,  142  miles  long,  afterwards  lengthened 
to  Brundisium,  a  total  of  360  miles,  was  perhaps  the  most 
famous  of  the  military  roads  radiating  from  the  capital  city. 
It  is  said  these  roads,  about  thirty,  extended  throughout  the 
entire  empire,  which  dominated  a  large  part  of  the  then  known 
world.  The  Roman  construction  was  massive  and,  not- 
withstanding they  were  used  for  hundreds  of  years  and  then 
neglected  after  the  fall  of  the  empire,  many  are  yet  in  such  a 


DEVELOPMENT   OF   ROAD   SYSTEMS  341 

state  of  preservation  that  their  method  of  construction,  con- 
sisting of  four  successive  courses  placed  upon  the  prepared 
subgrade,  may  be  still  seen.  Under  what  organization  the 
Romans  worked,  if  known,  is  of  no  particular  interest  at  the 
present  day. 

During  the  Dark  Ages,  road  building  in  Europe  fell  into 
desuetude ;  there  was  even  a  premium  upon  bad  roads  in  places 
for  the  robber  barons  had  enacted  laws  providing  that  the 
vehicle,  together  with  its  load,  which  broke  down  should  become 
the  property  of  the  person  upon  whose  land  the  accident 
occurred.  They  also  exacted  excessive  tolls  or  tariffs  for  passing 
over  their  domains.  Even  in  England,  according  to  Macaulay, 
the  conditions  were  extremely  bad,  the  roads  were  not  only  poor, 
but  highway  robbery  flourished.  A  prince  of  France  visiting 
in  England  had  to  have  footmen  go  ahead  with  lanterns  to  light 
the  way  while  others  followed  with  poles  to  pry  the  carriage  from 
the  numerous  mud  holes  encountered. 

In  the  last  quarter  of  the  eighteenth  and  the  first  quarter 
of  the  nineteenth  centuries  road  building  received  considerable 
impetus.  This  has  resulted  in  fine  paved  roads  throughout 
France,  Great  Britain,  Switzerland,  Germany,  and  most  of 
the  other  European  countries. 

The  United  States. — While  some  progress  was  made  during 
colonial  times,  it  was  usual  merely  to  clear  away  the  brush  and 
blaze  the  trees  that  the  way  might  be  followed  by  horseback 
riders.  The  settlements  were  mostly  near  the  water— sea,  river, 
or  lake,  upon  which  by  boat  commerce  was  carried.  The 
York  road  between  New  York  City  and  Philadelphia  was  laid 
out  in  1711.  During  the  French  and  Indian  War  some  mili- 
tary roads  were  established  across  the  Allegheny  Mountains. 
George  Washington  laid  out  one  in  1754,  over  which  passed 
Colonel  Fry's  army.  In  1755  General  Braddock  followed 
approximately  the  same  trail. 

Constitutional  Provision. — The  framers  of  the  Constitution 
provided  for  governmental  construction  and  management  of 
post  roads.  But  the  government  did  nothing  to  that  end  until 
the  construction  of  the  National  or  Cumberland  road.  Mean- 


342     REVENUE,   ADMINISTRATION   AND   ORGANIZATION 

while  a  number  of  private  corporations  were  chartered  by  the 
several  States  to  build  turnpikes.  These  were  allowed  to  exact 
toll  for  the  privilege  of  traveling  upon  them. 

The  Lancaster  Turnpike,  which  extended  from  Philadelphia 
to  Lancaster,  Pa.,  is  supposed  to  have  been  the  first  macadam 
road  in  the  United  States.  It  was  built  in  1792  of  stones  of  all 
sizes  thrown  together  and  covered  with  earth.  Later  it  was 
'reconstructed  of  stones  none  of  which  would  not  pass  a  2-inch 
ring.  Many  other  toll  roads  adopted  this  system.  By  1811 
317  turnpikes  had  been  chartered  in  New  York  and  the  New 
England  States,  being  about  4500  miles  of  road  with  a  com- 
bined capital  of  $7,500,000.  By  1828  there  had  been  3110 
miles  of  chartered  turnpike  in  Pennsylvania  completed  at  a 
cost  of  over  $8,000,000. 

The  Cumberland  Road. — Congress  appropriated  $30,000 
which  on  March  29,  1806,  was  approved  by  President  Thomas 
Jefferson,  to  be  used  for  the  survey  and  construction  of  a  road 
leading  from  a  point  on  the  Potomac  at  or  near  Cumberland  to 
the  Ohio  River  at  or  near  the  town  of  Steubenville.  This 
measure  was  sponsored  by  such  men  as  Henry  Clay  and  Albert 
Gallatin.  It  provided  that  the  road  be  cleared  for  a  width  of 
4  rods,  and  that  no  grade  exceed  5%.  In  1820  $10,000  was 
appropriated  by  Act  of  Congress  to  lay  out  a  road  from  Wheel- 
ing, Va.,  to  the  Mississippi  River  near  St.  Louis.  This  was  a 
continuation  of  the  Cumberland  or  National  Road,  and  was 
laid  out  80  feet  wide.  Appropriations  were  made  from  tune  to 
time  for  this  highway,  the  last  direct  appropriation  being  made 
for  a  portion  west  of  the  Ohio,  May  25,  1838.  The  total  appro- 
priations amounted  to  $6,824,919.33.  The  money  came 
largely  from  the  sale  of  public  land.  From  1835  to  1850,  little 
by  little  the  government  gave  over  the  management  of  the  road 
to  local  turnpike  companies.  At  the  present  time  it  has  prac- 
tically all  been  taken  into  the  State  highway  systems.  This 
ambitious  road-building  project  by  the  nation  ended,  after  the 
advent  of  the  steam  railway,  upon  the  prairies  of  Illinois.  It 
had  been  surfaced  to  Columbus  and  west  of  there  in  places. 
Had  it  not  been  for  the  phenomenal  growth  of  the  "railways 


FEDERAL  AID  343 

and  their  ability  to  transport  goods  and  passengers  quicker  and 
cheaper  than  the  highways  there  is  no  doubt  but  what  large 
systems  of  the  latter  covering  the  entire  settled  portion  of  the 
country  would  have  been  developed. 

Later  Developments. — The  United  States  government  has 
since  done  little  in  actual  road-building.  Some  roads  have  been 
constructed  in  the  island  possessions  and  some  in  the  national 
parks  and  forest  reserves.  The  Federal  Aid  Road  Bill  became  a 
law  on  July  11,  1916.  By  this  law  the  sum  of  $85,000,000  is 
made  available  for  the  construction  of  rural  roads  in  the  United 
States.  The  sum  of  $75,000,000  is  to  be  expended  for  the 
construction  of  rural  post  roads  under  co-operative  arrange- 
ments with  the  highway  departments  of  the  various  States, 
and  $10,000,000  is  to  be  expended  for  roads  and  trails  within 
or  partly  within  the  national  forests.  The  act  limits  the  Fed- 
eral Government's  share  in  road  work  in  co-operation  with  the 
states  to  50  per  cent  of  the  estimated  cost  of  construction. 
Federal  aid  is  extended  to  the  construction  of  rural  post  roads, 
excluding  all  streets  or  roads  in  towns  having  a  population  of 
2500  or  more,  except  the  portion  of  such  streets  or  towns  in 
which  the  houses  are  on  an  average,  more  than  200  feet  apart. 
Five  million  dollars  is  made  available  for  expenditure  during 
the  fiscal  year  ending  June  30,  1917,  and  thereafter  the  appro- 
priation is  increased  at  the  rate  of  $5,000,000  a  year  until 
1921,  when  the  sum  provided  is  $25,000,000,  making  a  total  of 
$75,000,000.  In  addition  an  appropriation  of  $1,000,000  a 
year  for  ten  -years  makes  up  that  part  to  be  devoted  to  roads 
within  the  forest  reserves. 

The  act  provides  that  after  making  necessary  deductions 
for  administering  its  provisions  in  not  to  exceed  3  per  cent  of  the 
appropriations  for  any  one  fiscal  year — the  Secretary  of  Agri- 
culture shall  apportion  the  remainder  of  each  year's  appro- 
priation in  the  following  manner : 

One-third  in  the  ratio  which  the  area  of  each  State  bears  to  the  total 
area  of  all  the  States. 

One -third  in  the  ratio  which  the  population  of  each  State  bears  to  the 
total  population  of  all  the  States. 


344     REVENUE,   ADMINISTRATION   AND   ORGANIZATION 

One-third  in  the  ratio  which  the  mileage  of  rural  delivery  routes  and 
star-routes  in  each  State  bears 'to  the  total  mileage  of  rural  delivery  routes 
and  star-routes  in  all  the  States. 

The  Secretary  of  Agriculture  promulgated  rules  and  regu- 
lations 1  for  carrying  out  the  act  which  provide  for  a  very  close 
supervision  by  the  Office  of  Public  Roads  and  Rural  Engineer- 
ing for  the  expenditure  of  the  money.  Any  State,  county  or 
district  making  application  for  aid  must  present  a  "  Project 
Statement "  to  enable  the  Secretary  to  ascertain  (a)  whether 
the  project  conforms  to  the  requirement  of  the  Act;  (6)  whether 
adequate  funds,  or  their  equivalent,  are  or  will  be  available 
by  or  on  behalf  of  the  State  for  construction;  (c)  what  pur- 
pose the  project  will  serve  and  how  it  correlates  with  the  other 
highway  work  of  the  State;  (d)  the  administrative  control  of, 
and  responsibility  for,  the  project;  (e)  the  practicability  and 
economy  of  the  project  from  an  engineering  and  construction 
standpoint;  (/)  the  adequacy  of  the  plans  and  provisions  for 
maintenance  of  roads;  and  (g)  the  approximate  amount  of 
Federal  aid  desired."  Forms  of  contract  together  with  all 
documents  referred  to  in  them  must  also  be  submitted.  Projects 
are  to  be  recommended  in  the  order  of  their  application.  Rules 
are  also  established  for  plans,  sketches,  maps,  estimates,  and 
other  things.  It  also  provides  that  the  materials  should  be 
tested  before  use,  that  no  part  of  the  right  of  way  shall  be  paid 
for  by  government  funds,  that  complete  records  and  cost  data 
shall  be  kept,  and  the  method  of  payments  is  specified. 

STATE  AID 

The  State  aid  principle  has  been  in  use  in  Europe  for  upwards 
of  a  century  but  was  first  adopted  in  the  United  States  in  1891. 
At  a  mass-meeting  of  farmers  and  others  interested  in  roads 
called  by  the  State  Board  of  Agriculture  of  New  Jersey,  in 
1887,  a  committee  was  appointed  to  examine  the  laws  of  their 
own  State,  of  other  States  and  foreign  countries,  and  report 

1  Rules  and  Regulations  for  Carrying  out  the  Federal  Aid  Road  Act, 
Circular  No.  65,  U.  S.  Dept.  of  Agriculture. 


STATE  AID  345 

such  amendments  as  in  their  judgment  would  best  serve  the 
interests  of  the  commonwealth.  The  committee  held  meetings 
and  studied  many  laws;  after  careful  consideration,  they 
recommended  the  abolishment  of  the  office  of  road-overseer. 
As  a  result  the  board  of  agriculture  had  a  bill  prepared  and  pre- 
sented in  the  State  legislature  of  1888  to  that  effect.  Through 
the  influence  of  the  overseers  this  bill  was  defeated;  it  was 
again  introduced  in  1889  and  again  defeated;  and  met  with  a 
similar  fate  in  1890.  But  in  1891  its  friends  succeeded  in  secur- 
ing its  passage.  The  plan  of  placing  the  roads  under  the  town- 
ship committees  proved  so  successful  that  the  opposition  was 
not  only  unable  to  effect  its  repeal,  although  a  -trial  was  made, 
but  the  State  went  farther  in  the  line  of  centralization  by  enter- 
ing upon  an  entirely  new  departure.  This  new  law,  passed  in 
1891  and  made  operative  in  1892,  is  what  is  commonly  called 
the  State  Aid  Law,  a  law  which  has  influenced  legislation  in 
nearly  all  the  States  of  the  Union.  The  following  quotation 
from  the  first  state  aid  law  gives  the  salient  features : 

That  whenever  there  shall  be  presented  to  the  board  of  chosen  free 
holders  of  any  county  a  petition  signed  by  the  owners  of  at  least  two- 
thirds  of  the  land  .  .  .  fronting  on  any  public  road  .  .  .  praying  the  board 
to  cause  such  to  be  improved  and  setting  forth  that  they  are  willing  the 
peculiar  benefits  conferred  .  .  .  shall  be  assessed  thereon  in  proportion 
to  the  benefits  conferred  to  an  amount  not  exceeding  10  per  centum  of 
the  entire  cost  of  improvement  ...  it  shall  be  the  duty  of  the  board  to 
cause  such  improvements  to  be  made  .  .  .  That  one-third  of  the  cost  of 
all  roads  constructed  under  this  act  shall  be  paid  for  out  of  the  state 
treasury. 

Under  this  first  act  the  abutting  property  holders  paid 
one-tenth  the  cost,  the  State  one-third  and  the  county  the 
remaining  56f  per  cent.  The  friends  of  the  law  demanded  its 
enforcement,  the  opponents  as  strenuously  objected  and  car- 
ried the  matter  into  the  courts,  but  the  law  was  upheld.  A 
few  changes  only  have  been  made  in  the  law,  these  tending 
to  its  more  efficient  administration,  the  most  important  being 
the  authorization  of  a  State  highway  commissioner. 

In  1893  Massachusetts  adopted  a  similar  law.  Under  this 
law  the  State  bears  75  per  cent  and  the  county  25  per  cent  of  the 


346     REVENUE,   ADMINISTRATION   AND   ORGANIZATION 

cost  of  improvement.  In  1895  Connecticut  adopted  the  State 
aid  principle,  and  New  York  in  1898.  Without  mentioning 
further  dates  it  may  be  said  that  the  State  aid  principle  in  some 
one  of  its  various  forms  is  in  operation  in  nearly  all  the  States 
in  the  Union.  A  great  many  States  supply  cash  aid  in  varying 
amounts,  others  supply  engineering  services,  plans,  specifica- 
tions, or  give  aid  in  the  use  of  convicts. 

STATE  HIGHWAY  DEPARTMENTS 

While  the  details  of  carrying  out  State  aid  differ  with 
different  States,  all  have  State  highway  departments.  Some 
consist  of  a  single  salaried  commissioner,  or  engineer,  appointed 
by  the  governor,  or  elected  by  the  people ;  others  an  unsalaried 
commission  either  appointed  or  ex-officio  heads  of  departments 
of  State  or  State  educational  institutions;  and  in  others  a  sal- 
aried commission  of  three  or  more  persons  appointed  or  elected. 
A  centralized  administration  makes  for  efficiency.  Authority 
for  doing  things  is  placed  upon  one,  or  at  the  most,  a  few  per- 
sons. There  is  no  chance  to  escape  responsibility.  System- 
atic organization  is  likewise  essential  for  best  results.  Every 
under  officer  down  to  road  caretaker  should  know  exactly  what 
is  expected  of -him  and  how  far  his  authority  extends. 

Powers. — State  highway  departments  are  usually  empow- 
ered to  map  the  various  soil  areas  of  the  State,  to  study  the 
character  of  each  for  road  purposes,  to  devise  means  of  con- 
struction and  maintenance  best  adapted  to  the  different  soils, 
to  determine  whether  or  not  a  mixture  of  soils  from  different 
areas  would  be  advantageous,  to  seek  out  and  test  gravel, 
stone,  and  other  materials  available  to  the  several  portions  of 
the  State  and  to  publish  the  results  of  the  investigations.  In 
some  States  the  department  furnishes  uniform  or  standard  plans 
for  road  construction,  maintenance,  culverts,  bridges,  guard 
rails,  railroad  crossings,  etc.  This  makes  it  possible  to  com- 
pare unit  costs,  a  thing  highly  desirable,  and  to  prevent  over- 
charge and  scandal, 


STATE   HIGHWAY   LAWS  347 


STATE  HIGHWAY  LAWS 

While  each  of  the  several  States  has  its  own  peculiar  prob- 
lems and  laws,  space  will  not  permit  of  separate  treatment. 
The  tendency  seems  to  be  toward  a  classification  of  highways 
into  main  and  less  traveled  roads.  The  main  roads  may  be 
denominated  "  State "  highways  in  contradistinction  to 
"  county  "  and  "  township  "  for  those  less  traveled.  In  order 
that  the  main  traveled  roads  may  be  combined  into  a  com- 
prehensive system  so  connecting  the  various  parts  of  the  State 
that  lines  of  travel  may  be  as  direct  as  is  consistent  with  other 
conditions,  it  is  the  duty  of  the  State  to  provide  for  some  cen- 
tralized authority  over  the  main  traveled  roads,  leaving  to 
local  control  those  of  less  importance.  This  idea  has  led  to 
the  formation  of  highway  commissions  and  more  or  less  com- 
plete and  complex  organizations  under  them. 

State  Highway  Commissions. — In  a  number  of  the  States 
the  highway  commission  consists  of  a  single  person,  in  others 
of  several  persons  forming  a  board  of  commissioners.  In  at 
least  one  State  the  highway  commissioner  is  elected  by  the 
voters  "  in  the  same  manner  as  justices  of  the  supreme  court." 
In  many  States  the  commissioners  are  appointed  by  the  gov- 
ernor, with  or  without  the  consent  of  the  Senate.  In  others 
the  commission  is  made  up  ex-officio  of  other  State  officers,  of 
specified  members  of  the  faculty  of  the  State  university,  or  of 
both  combined.  . 

While  there  are  arguments  favoring  centralizing  authority 
for  the  sake  of  efficiency  in  a  single  person,  local  conditions 
may  make  this  inconvenient,  and  where  considerable  money  is 
being  handled  it  is  usually  more  satisfactory  if  two  or  more 
persons  are  made  responsible  for  its  management.  However, 
good  work  is  being  done  under  all  these  forms  of  organization. 

State  Highway  Engineer. — Where  there  is  a  board  of  com- 
missioners, they  usually  deal  personally  only  with  matters  of 
general  policy,  leaving  the  details  to  a  State  highway  engineer, 
who,  in  some  States  is  appointed  for  a  specified  term,  in  others 
holds  office  at  the  pleasure  of  the  commission. 


348     REVENUE,    ADMINISTRATION   AND   ORGANIZATION 

Typical  Laws  for  the  Formation  of  Highway  Departments, 
quoted  from  the  statutes  of  two  States,  illustrate  the  one- 
person  commission  and  the  multiple-person  commissions. 

From  the  Ohio  Laws: 

The  State  highway  commissioner  shall  have  general  supervision  of  the 
construction,  improvement,  maintenance  and  repair  of  all  inter-county 
highways  and  main  market  roads,  and  the  bridges  and  culverts  thereon. 
He  shall  aid  the  county  commissioners  in  establishing,  creating  and  pre- 
paring suitable  systems  of  drainage  for  highways,  and  advise  with  them  as 
to  the  construction,  improvement,  maintenance  and  repair  of  highways; 
and  he  shall  approve  the  design,  construction,  maintenance  and  repair  of 
all  bridges,  including  superstructure  arid  substructure,  and  culverts  or 
other  improvements  on  inter-county  or  main  market  roads;  and  in  the  case 
of  bridges  and  culverts  on  .other  roads,  when  the  estimated  cost  thereof 
exceeds  $10,000,  the  plans  therefor  shall  be  submitted  to  and  approved  by 
him,  before  contracts  are  let  therefor.  He  shall  cause  plans,  specifications 
and  estimates  to  be  prepared  for  the  construction,  maintenance  or  repair 
of  bridges  and  culverts  when  so  requested  by  the  authorities  having  charge 
thereof,  and  he  shall  cause  to  be  made  surveys,  plats,  profiles,  specifica- 
tions and  estimates  for  improvements  whether  upon  State,  county  or 
township  roads.  He  shall  make  inquiry  in  regard  to  systems  of  road  and 
bridge  construction  and  maintenance  whenever  he  may  deem  it  advisable, 
and  conduct  investigations  and  experiments  with  reference  thereto,  and 
make  all  examinations,  in  his  opinion,  advisable,  as  to  materials  for  road 
construction  or  improvement. 

From  the  North  Carolina  laws: 

The  State  highway  commission  shall  consist  of  the  governor,  three  citi- 
zens of  the  State  of  North  Carolina  to  be  appointed  by  the  governor,  one 
from  the  eastern,  one  from  the  central,  and  one  from  the  western  portion 
of  the  State,  one  of  whom  shall  be  a  member  of  the  minority  political  party, 
the  State  geologist,  a  professor  of  civil  engineering  of  the  University  of 
North  Carolina  and  a  professor  of  the  North  Carolina  Agricultural  and 
Mechanical  College,  said  professors  to  be  designated  by  the  governor. 
The  members  of  the  commission  shall  be  appointed  and  serve  for  four 
years,  and  until  their  successors  are  appointed;  the  members  of  the  com- 
mission shall,  when  employed  in  any  manner  required  of  them  under  this 
act,  receive  their  actual  expenses.  The  governor  shall  fill  all  vacancies 
in  the  commission  caused  by  death  or  otherwise,  and  he  shall  have  the 
power  to  remove  any  member  for  due  cause. 

Duties  of  Highway  Departments. — From  a  review  of  the 


TYPICAL  HIGHWAY  LAWS  349 

legislation    concerning    State    highway    departments    by    R. 
Walton  Moore  is  taken  the  following: 1 

Miscellaneous  Duties,  (a)  Lease  offices;  (6)  purchase  furniture  and 
office  and  engineering  supplies;  (c)  engage  assistants,  employ  skilled  and 
unskilled  labor,  and  utilize  convicts  and  prisoners;  (d)  maintain  facilities 
for  testing  materials  used  in  road  and. bridge  construction,  and  investigate 
sources  and  properties  of  such  materials;  (e)  issue  permits  for  occupation 
of  State  and  State-aid  roads  by  trucks,  pole  lines,  conduits  and  other 
structures;  (/)  collect  automobile  fees  and  issue  regulations  governing 
the  use  of  vehicles  on  public  roads;  (g)  issue  regulations  for  use  of  State 
and  State-aid  roads  by  traction  engines,  motor  omnibuses  and  trucks; 
(h)  institute  suitable  legal  proceedings  to  stop  violations  of  highway  and 
bridge  statutes;  (i)  conduct  investigations  and  collect  statistics  of  traffic; 
(./)  keep  detailed  records  of  the  expenditure  of  all  State  road  and  highway 
bridge  funds;  (fc)  give  names  to  through  routes  and  mark  them  or  permit 
them  to  be  marked  by  colors  and  signs;  (/)  to  acquire  toll  roads,  bridges 
and  ferries. 

Educational  Duties,  (a)  Collect  information  relating  to  roads  and  high- 
way bridges  in  the  State;  (6)  investigate  the  suitability  of  different  types 
of  road  and  bridge  construction  for  use  in  the  State;  (c)  hold  public  meet- 
ings to  explain  the  desirability  of  road  and  bridge  improvements;  (d}  hold 
meetings  with  county  and  township  road  officials  to  discuss  the  improve- 
ment and  maintenance  of  roads  and  bridges;  (e)  publish  annual  reports 
of  the  department's  work  and  bulletins  on  subjects  relating  to  the  con- 
struction and  maintenance  of  roads  and  bridges;  (/)  notify  local  officials 
of  road  and  bridge  work  which  is  being  done  in  a  wasteful  manner,  and  if 
the  wasteful  methods  are  continued  report  them  to  the  governor;  (g) 
prepare  standard  plans  and  specifications  for  roads  and  bridges. 

State  Road  Duties. — (a)  Determine  the  main  roads  of  the  State  and  pre- 
pare maps  of  them;  (6)  designate  the  order  in  which  main  roads  shall  be 
improved  with  State  funds;  (c)  acquire  rights  of  way  by  contract  or  con- 
demnation proceedings;  (d)  prepare  plans  and  specifications  for  roads  and 
bridges  built  by  State-aid  and  supervise  their  construction;  (e}  make 
contracts  for  State  road  and  bridge  improvements  and  maintenance; 
(/)  carry  on  construction  and  maintenance  of  State  roads  and  bridges  with 
day  labor,  both  free  and  convict;  (g)  buy  or  hire  machinery,  tools,  mate- 
rials, teams  and  supplies  needed  in  carrying  the  work  of  the  department. 

Co-operatwe  Duties. — (a)  Prepare  or  aid  in  preparing  plans  for  road 
or  bridge  improvements  by  local  officials;  (6)  supervise  or  assist  in  super- 
vising construction  and  maintenance  of  roads  under  local  officials;  (c) 

1  "Review  of  Legislation  Concerning  State  Highway  Departments," 
by  R.  Walton  Moore,  published  by  the  American  Highway  Association, 
1916,  Washington,  D.  C. 


350     REVENUE,   ADMINISTRATION   AND   ORGANIZATION 

apportion  among  the  counties  or  other  subdivisions  State  funds  for  co-op- 
erative road  and  bridge  work;  (d)  act  with  local  authorities  in  designating 
road  and  bridge  work  on  which  State  funds  shall  be  spent;  (e)  approve 
contracts  for  road  and  bridge  work  made  by  local  officials;  (/)  hold  com- 
petitive examinations  for  positions  of  county  highway  superintendents  or 
engineers  to  furnish  lists  of  capable  men  from  which  counties  must  select 
such  officials;  (g)  approve  plans  for  road  and  bridge  improvements  sub- 
mitted by  local  officials;  (h)  determine  when  State-aid  roads  are  improperly 
maintained,  in  case  the  law  prohibits  further  State  aid  to  counties  where 
State-aid  roads  are  not  kept  in  satifactory  condition  by  the  counties; 
(i)  inspect  annually  all  bridges  exceeding  30  feet  in  length  and  advise 
local  authorities  of  their  condition;  (.;')  prepare  and  distribute  directions 
and  forms  for  accounting  for  local  road  funds  and  recording  all  official 
actions  of  local  road  authorities. 

These  cover  compactly  the  duties  delegated  to  the  highway 
departments  in  the  United  States.  Perhaps  no  one  State  would 
burden  its  department -with  all  of  them  but  only  with  such  as 
are  appropriate  to  the  local  conditions  in  that  State. 

Organization  Charts. — An  organization  chart  is  a  graphical 
representation  of  the  total  business  into  its  component  parts 
and  is  built  up  somewhat  after  the  manner  of  a  genealogical 
tree.  A  complete  chart  indicates  exactly  through  whom 
authority  reaches  from  the  head  to  the  lowest  subordinate, 
and  each  person  knows  to  whom  he  shall  look  for  instructions 
and  to  whom  he  in  turn  shall  give  instructions.  It  assists  in 
avoiding  conflicts  of  authority  or  the  short-circuiting  of  orders. 
The  making  of  such  a  chart  in  itself  is  a  long  step  toward  sys- 
tematizing the  work  of  a  department,  and  system  means  effi- 
ciency and  economy. 

Each  State  highway  department  will  work  out  its  own  chart 
compatible  with  its  own  needs  and  limitations.  A  few  such 
charts  are  given  as  examples,  pp.  351-354. 

COUNTY  AND  TOWNSHIP  ORGANIZATION 

County  and  township  road  organization  varies  so  greatly 
in  the  several  States  that  it  is  not  possible  to  generalize  with 
any  degree  of  accuracy.  In  many  States  the  local  road  admin- 
istration is  under  a  county  board  of  supervisors  or'  commis- 


ORGANIZATION  CHARTS 


351 


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354     REVENUE,   ADMINISTRATION  AND  ORGANIZATION 


PEOPLE 
LEGISLATURE,  GOVERNOR,ETC. 


SUPERVISORY  AU- 
THORITIES PUNITIVE 
INSTITUTIONS 


STATE  HIGHWAY  DEPARTMENT 


COUNTY  BOARD 

OR 

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TOWNSHIP  ORGANIZATION 


TOWNSHIP  TRUSTEES 


TOWNSHIP  HIGHWAY  SUPT 


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— \  CONTRACTS  AHP  CONTRACTORS  J 
FIG.  173. — Typical  Township  and  County  Organization 


COUNTY  AND   TOWNSHIP  ORGANIZATION  355 

sioners,  or  under  the  direction  of  the  county  court.  In  other 
States  there  is  a  smaller  unit,  the  township,  with  township 
trustees.  The  county,  or  the  township,  is  also  sometimes 
divided  into  road  districts  and  an  overseer  appointed  or  elected 
to  look  after  the  roads  of  the  district.  In  extreme  cases  the  road 
districts  are  independent  units  and  have  power  to  levy  taxes 
on  the  property  of  the  district.  In  other  States  a  more  com- 
prehensive organization  is  effected  in  which  practically  all  roads 
are  under  the  supervision  of  the  State  highway  department,  or 
of  the  State  and  county  officers  jointly. 

The  tendency  seems  to  be  toward  centralized  organization, 
certain  roads  being  designated  "State  highways"  and  their 
construction,  and  sometimes  maintenance,  given  over  to  the 
State  department.  These  roads  share  in  the  State  aid  money 
received  from  taxation,  automobile  licenses  or  Federal  appro- 
priations. Other  roads  are  designated  as  county  roads  and  left 
under  the  supervision  of  the  county  officers.  Many  States 
have  laws  requiring  the  selection  of  a  county  engineer  (or  a 
county  surveyor  who  shall  be  county  road  superintendent)  and 
to  him  is  given  the  selection  and  charge,  to  a  greater  or  less 
degree,  of  the  minor  road  officers.  The  county  engineer  usually 
reports  to  the  county  board  and  to  the  State  highway  depart- 
ment. A  typical  organization  chart  for  township  and  county 
organizations  is  given  on  page  354, 


CHAPTER  XVI 
MISCELLANEOUS 

Road  Signs  and  Emblems. — Some  States  are  systematically 
laying  out,  mapping  and  marking  their  main  or  trunk  line  roads, 
both  as  a  convenience  in  filing  records  in  the  office  and  as  an 
aid  to  travelers.  Fig.  174  (c)  shows  the  authentic  mark 
adopted  by  Wisconsin.  Smaller  units,  such  as  counties,  are 


Detroit  Lincoln 
Denver  Highway 


(6) 

Untoln  Highway 


Wisconsin 
Trunk  Highways 


FIG.  174.— Typical  Telephone  Pole  Road  Markers. 


likewise  marking  their  roads.  Fig.  175  shows  a  form  of  con- 
crete sign  adopted  by  Lancaster  county,  Nebraska,  designed 
by  county  engineer  A.  H.  Edgren.  Fig.  176  gives  the  details 
of  construction.  Reversed  letter  patterns  are  attached  to  the 
inside  of  the  form  so  that  when  the  form  is  removed  the  letters 
are  sunk  into  the  concrete.  The  surface  coating  of  the  sign  is 

356 


ROAD   SIGNS 


357 


made  of  white  cement  and  white  sand  plastered  on  the  inside 
of  the  form  before  the  ordinary  concrete  of  the  interior  is  placed. 


FIG.  175. — Edgren's  Concrete  Sign  Post. 

The  letters  are  painted  black  with  a  waterproof  paint, 
designs  of  markers  are  shown  in  Figs.  176  to  179. 


Other 


358 


MISCELLANEOUS 


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FIG.  176. — Standard  Concrete  Road  Markers,  Lancaster  Co.,  Nebraska. 


'Fie.  177. — A  Simple  Concrete  Road  Marker. 


CONCRETE  SIGN  POSTS 


359 


Volunteer  road  organizations  have  marked  long,  even  trans- 
continental routes  across  the  country.     Individual  routes  are 


FIG.  178. 


FIG.  179. 


Concrete  Sign  Posts 


usually  marked  by  an  emblem  or  insignia.     Many  States  now 
provide  for  the  registering  of  these  emblems  and  protect  the 


360 


MISCELLANEOUS 


route  in  the  use  of  them.  The  route  emblem  or  mark  is  con- 
veniently placed  upon  the  telephone  poles  along  the  road  so 
that  the  tourist  though  a  stranger  can  readily  follow  the  way. 
Fig.  174  shows  such  emblems. 

Sign  posts  are  also  placed  at  crossroads  to  direct  to  par- 
ticular localities.  Steel  boards  with  the  letters  pressed  into 
them  or  spot  welded  upon  them,  or  made  by  drilling  holes 
through  them  are  now  manufactured  and  placed  upon  the 
market.  The  steel  board  has  the  advantage  over  wood  of  being 
not  only  durable,  but  less  liable  to  injury  by  the  vandalic 


FIG.  180.— Iowa  State  Detour  Signs. 


sportsman's  shotgun.  Warning  signs  of  dangerous  crossings 
and  bridges,  nearness  to  schools  and  hospitals,  of  impassable 
roads  ahead,  and  markers  calling  attention  to  points  of  his- 
torical or  scenic  interest  along  the  route  are  also  furnished  and 
set  up,  both  by  public  and  private  means. 

Detour  Signs. — Roads  must  frequently  be  closed  to  travel 
on  account  of  construction,  repairs,  maintenance,  washouts, 
and  obstructions  of  various  kinds.  At  such  times  the  traveling 
public  is  entitled  to  notice  and  directions  how  to  avoid  the 
impediment  with  the  least  delay.  The  Iowa  State  Highway 
Commission  has  adopted  standard  directions  for  such  signs 


PLACING  THE  SIGNS 


361 


stating  distinctly  upon  whom  the  responsibility  for  their  setting 
up  and  maintenance  rests  and  the  fund  from  which  the  expenses 
must  be  paid.  Upon  primary  (State)  roads  the  district  engi- 
neer, and  upon  county  roads  the  county  engineer  will  be  held 
accountable  for  the  following: 

First. — He  shall  determine  whether  or  not  a  detour  is  needed. 
Second. — He  shall  co-operate  with  the  local  officials  in  choosing  a  detour. 
Third. — He  shall  provide  for  the  proper  marking  of  the  detour. 
Fourth. — He  shall  provide  for  the  maintenance  of  the  detour  and  report 
such  provision  to  the  central  office. 


FIG.  181. — Typical  Arrangement  of  Detour  Signs 

Since  great  care  should  be  exercised  in  selecting  the  best 
possible  detour  engineers  are  always  to  consult  with  county 
boards. 

Placing  the  Signs. — The  signs  are  placed,  Fig.  181,  on  the 
right-hand  side  of  the  road  at  the  far  side  of  the  intersection; 
the  arrow  will  point  away  from  the  intersection  and  give  a 
positive  direction.  In  order  that  the  signs  may  be  made  up  in 
quantities,  the  word  "  Detour  "  is  printed  in  both  directions, 
Fig.  180.  The  one  which  is  upside  down  after  the  sign  is  placed 
is  to  be  painted  out.  The  names  of  the*  towns  may  be  painted 
or  stenciled  in  if  desired.  A  substantial  barricade  with  the 
word  "  Closed  "  is  placed  across  the  road,  also  a  "  slow  down  " 
sign  some  300  feet  away  on  the  right-hand  side  of  the  roadway. 


362 


MISCELLANEOUS 


ROAD  MAINTENANCE  COMPETITION 

Score  Card  for  Road  Maintenance  Contests. — In  some 
places  a  friendly  rivalry  has  been  established  for  the  main- 
tenance of  rural  roads.  The  score  card  below  is  one  devised 
by  Professor  L.  W.  Chase  for  use  in  Fillmore  County,  Nebraska ; 
it  gives  also  the  score  and  rank  of  several  roads  for  the  season 
of  1916. 

SCORE    CARD    FOR   FILLMORE    COUNTY    ROADS 


ELEMENTS  GIVEN  CONSIDERATION 

Dis- 

Overseer's Name 

Sur- 
face 

Width 

Crown 

Gut- 
ters 

tribu- 
tion 
of 

Drain- 
age 

Park- 
ing 

Total 

Rank 

Traffic 

Perfect  score 

20 

20 

20 

15 

10 

10 

5 

100 

Hansen,  Henry.  .  .  . 

16 

10 

20 

14 

8 

9 

4 

81 

1st 

Klatt,  John  

15 

20 

15 

13 

5 

8 

4 

80 

2d 

Kieser,  C.  H  

17 

20 

15 

10 

8 

7 

2 

79 

3d 

19 

20 

15 

7 

10 

5 

2 

78 

4th 

18 

18 

8 

2 

8 

2 

5 

61 

5th 

17 

0 

5 

0 

0 

0 

5 

27 

6th 

Government  Road  . 

20 

18 

20 

12 

10 

9 

1 

90 

FIG.  182. — Score  Card  for  Road  Competition 

•  Rating  Local  Road  Superintendents. — A  variation  of  the 
above  as  a  means  to  promote  competition  among  road  super- 
intendents is  used  by  W.  G.  Tonkel,  county  highway  superin- 
tendent of  Allen  county,  Indiana.  The  blank  form  used  by 
Mr.  Tonkel,  Fig.  183,  is  self  explanatory. 

RACE  TRACKS 

The  shape  of  race  tracks  have  been  standardized  by  the 
various  organizations  using  them.  The  county  agricultural 
societies  generally  have  a  half-mile  track,  while  State  societies 
and  other  more  ambitious  organizations  have  mile  tracks. 


MAINTENANCE  COMPETITION 


363 


DISTRICTS 


l. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 
10. 
11. 
12. 
13. 
14. 
15. 
16. 
17. 
18. 
19. 
20. 
21. 
22. 
23. 
24. 
25. 
26. 
27. 
28. 
29. 
30. 
31. 
32. 
33. 


Grading  of 
Road  Superintendents 

of  Allen  County,  Indiana 

The  four  leading  elements  con- 
sidered in  maintaining  County 
Highways  are: 

No.  1.  Grading,  Dragging  25% 

No.  2.  Crown  and  Bermes 

of  Road      -      -        25% 

No.  3.  Ditches,  Drainage  25% 

No.  4.  Management  of 

District      -      -       25% 

100% 


TOTAL 


Date  19.-. 

District  No. 

Supt 

Graded  by 

Remarks 


FIG.  183. — Blank  Used  in  Grading  Work  of  District  Road  Superintendent. 


364 


MISCELLANEOUS 


Since  the  advent  of  the  motor  car  still  longer  tracks  are  being 
constructed. 

The   surface    of   the   ordinary  track  is  earth.     Horsemen 


FIG.  184. 

prefer  a  sandy  loam  containing  considerable  humus  in  the  form  of 
fine  rootlets.     This  gives  resiliency,   thus  making  a   "  fast  " 


FIG.  185.— Standard  Mile  Track. 

The  width  is  not  standardized.     The  length  ia  measured  on  the  pole  line  3  ft.  outside 
of  the  inner  edge. 

track.  After  a  track  has  been  used  for  many  years  and  main- 
tained by  dragging,  the  surface  becomes  thoroughly  puddled, 
hard  and  unyielding;  it  is  then  said  to  be  "  dead  "  and  is  cured 


MAINTENANCE   COMPETITION 


365 


by  removing  the  surface  and  replacing  it  with  fresh  field  loam. 
That  immediately  under  the  top  sod  in  a  clover  field  is  recom- 
mended. 

For  automobile  tracks  the  surface  is.best  when  hard  and 
smooth.     Such  tracks  are  often  surfaced  with  plank,  concrete, 


Grand  Stand 


2  ml.  Lint 


20  10  0   J10'  20   30  40  50   60 

Elevation  of  outer  edge 

oftrac'fi,  a  on  curve, 

b,  on  ^traight-away 


FIG.  186. — Two  Mile  Speed-way,  Minneapolis-St.  Paul,  Minn. 

or  brick,  and  are  banked  or  inclined  toward  the  center  of  the 
curves  much  more  than  are  horse  tracks. 

The  design  of  standard  tracks  is  such  that  one-half  the 
distance  is  on  the  curve  and  one-half  along  the  straight-away. 
The  length  of  the  track  is  measured  along  the  pole  line  which  is 
3  feet  from  the  inner  fence.  Plans  of  race  tracks  are  shown  in 
Figs.  184,  185,  186. 


INDEX 


Abrams,  Duff,  A.,  249,  250,  256. 
257,  272 

Abrams'  fineness  modulus  method  in 
concrete  mixing,  249 

Administration,  constitutional  pro- 
vision, 341 

— ,  Cumberland  road,  342 

— ,  development  of  road  system,  340 

— ,  in  United  States,  341  . 

— ,  Lancaster  turnpike,  342 

— ,  later  developments,  343 

— ,  revenue,  and  organization  for 
road  construction,  333-355 

— ,  State  aid,  344,  345 

— , ,  Massachusetts,  345 

— , ,  New  Jersey,  344 

— ,  —  highway  departments,  346 

— , ,  powers,  346 

— , laws,  347-350 

— , ,  Commissions,  347 

• — , ,  duties  of  highway  de- 
departments,  348- 
350 

— , —  — ,  Engineer,  347 

— , ,  organization  charts, 

350 

— , ,  typical,  348 

Alignment  and  grades  of  earth  roads, 
125 

Arch  culverts,  116 

Asphalt  blocks,  83 

— ,  specifications  for,  table  of,  316 

melting-point  test,  295 

-  roads,  sheet,  314-321 

Attached  level,  64 


Automatic  concrete  measuring  de- 
vices, 268 
Automobile,  effect  of,  on  macadam, 

199 

—  race  tracks,  365 
Axman,  38 

B 

Back  sight,  39 
Bench  mark,  39 
Bituminized  brick,  231,  232 
Bituminous  macadam  roads,  82 

—  materials  for  surface  treatment, 

table  of,  330 

—  roads,  289-321 
,  asphalt  blocks,  321 

,  —  cement,  table  of  specifica- 
tions for,  316 

— ,  broken-stone,  300 

,  cement,  307 

,  — ,  proportioning,  309 

— ,  — ,  specifications  for,  302 

— ,  classification,  290 

— ,  concrete,  306-313 

— ,  — ,  classification,  306 

— ,  — ,  construction,  310-313 

— ,  — ,  definition,  306 
,  — ,  foundation,  310 

— ,  — ,  laying,  312 
-,  — ,  maintenance,  313 

— ,  — ,  materials,  307 

— ,  — ,  mixing,  311 
,  — /patented  mixtures,  306 

— ,  — ,  rolling,  312 

— ,  — ,  seal  coat,  313 

— ,  — ,  temperature  of  mixture, 

312 


367 


368 


INDEX 


Bituminous,     roads,     construction, 

302-306 

—  . — ,  — ,  crusher  run,  304 
— ,  — ,  maintenance,  303 

• ,  — ,  mechanically  mixed  filler, 

305 

,  — ,  sand-cement  mastic  layer, 

305 

,  — ,  seal  coat,  305 

,  — ,  subgrade,    drainage    and 

foundation  course,  302 

,  — ,  uniform  stone,  305 

,  — ,  voids,  partially  filled,  305 

,  — ,  wearing  surface,  304 

,  definitions,  290 

— ,  earth  roads,  298,  299 

— , ,  gravel,  300 

, ,  layer  method  of  con- 
struction, 299 

— , ,  oiled,  298 

— , ,  sand,  299 

— ,  macadam,  300,  301 

,  — ,  drainage  and  ^foundation, 

300 

,  — ,  mineral  aggregate,  300 

,  — ,  specifications,      alternate 

type,  301 

,  materials,  289 

,  native  asphalts,  291 

,  petroleum  asphalts,  292 

— ,  — ,  physical  and  chemical  tests, 

293-397 

, ,  consistency  test- 
penetration 
•   ,  ,  method,  293 

, ,  fixed  carbon, 297 

, ,  melting  -  point, 

cube  method, 
295 

, ,  — ,  ring  and  ball 

method,  295 

, ,  New  York  Test- 
ing Laboratory 
float  test,  294 


Bituminous  roads,  physical  and 
chemical  tests, 
solubility,  296 

,  — ,  viscosim  e  t  e  r 

method  of  test- 
i  n  g    consist- 
ency, 294 
•  — ,  sheet  asphalt,  314-321 

, ,  binder  course,  315 

— ,  —  — ,  definition,  314 

— , ,  filler,  317 

— ,  —  — ,  foundation,  314 
— ,  —  — ,  maintenance,  320 
— ,  —  — ,  mineral  aggregate,  317 
— ,  —  — ,  rock  asphalt,  320 

— , ,  sand,  317 

— , ,  standard  gradings,  ta- 
ble for,  318 

— ,  —  — ,  topping  mixture,  con- 
struction, 319 

— , , ,  design,  318,  319 

— , ,  wearing  course,  315 

,  sources  of  materials,  291,  292 

— ,  tars  and  pitches,  292 
Blind  drain,  93 
Block  roads,  211-232 
— ,  definition,  211 
— ,  stone,  225-228 
— ,  wood,  228-232 
Blocks,  asphalt,  321 
Bonds   for  road   construction,   an- 
nuity, 337-339 
— ,  serial,  336,  337 
Borrow  pits,  75,  140 
Box-culverts,  111 
Brick  roads,  83,  211-225 

,  design  and  construction,  217- 

221 

,  —        — ,  bituminous      filler, 

220 

, ,  concrete      founda- 
tions, 217 

— ,  -      -  — ,  curbing,  217 
, ,  expansion  joints,218 


INDEX 


369 


Brick   roads,  design  and   construc- 
tion, filler,  218 
— ,  —        — ,  foundation,  217 
— ,  —        — ,  grouting,  219 

— ,  — ,  laying    the    brick, 

218 

— ,  —  • ,  paint  coat,  221 

— , ,  pouring,  221 

— ,  -        — ,  rolling,  218 
— ,  —        — ,  sand  cushion,  218 
— ,  —        — ,  subgrade  and  drain- 
age, 217 

— ,  monolithic  brick  pavement, 
222-224 

, ,  bedding      method, 

222 

— , ,  direct  method,  222 

— , — ,  green  cement  meth- 
od, 223 

— ,  —        — ,  maintenance,  225 
— ,  —        — ,  inspecting  and  roll- 
ing, 224 

— ,  —        — ,  Paris    or    cement- 
sand  method,  222 
— ,  rattler  test  of   paving  brick, 

214 

— ,  scale  of  losses  in  paving  brick, 
215 

,  testing  paving  brick,  214-216 

— ,  visual    inspection   of    brick, 
215,  216 

,  vitrified  paving  brick,   211- 

213 
— ,   stone,   wood,   and  other  block 

roads,  211-232 

Bridges,  culverts  and,  103-122 
Broken-stone  roads,  181-201 

,  bituminized,  300 

— ,  construction,  190-198 

,  — ,  courses,  193 

,  — ,  cross-sections,  192 

,  — ,  macadam    road,     defini- 
tion, 191 
,  — ,  placing,  194,  195 


Broken-stone    roads,    construction, 

shoulders,  198 
— ,  — ,  subgrade,  190,  192 
— ,  — ,  telford    road,    definition, 

191 

— ,  — ,  upper  course,  197 
— ,  — ,  width   and    thickness   of 

macadam,  198 

— ,  crushers  and  screens,  200,  201 
— .,  maintenance,  198-200 
— ,  — ,  automobile,  effect  of,  on 

macadam,  199 

— ,  — ,  continuous  method,  198 
— ,  — ,  periodic  method,  199 
— ,  mineral  composition,  189 
— ,  rocks,  classification  of,  187- 
188 

— ,  — , ,  igneous,  188 

— ,  — ,  —  — ,  metaphoric  rocks, 

189 

— ,  — ,• ,  sedimentary  or  aque- 
ous, 188 

— ,  rocks,  principal  road,  189 
— ,  — ,  —  — ,  andesite,  189 

— ,  — , ,  basalt,  189 

— ,  — , ,  diabase,  189 

,  — , ,  diorites,  190 

— ,  — , ,  gneisses"  190 

,  — , ,  granites,  190 

— ,  — , ,  peridotite,  189 

— ,  — ,  —  — ,  syenites,  190 

— ,  — , ,  trap,  189 

,  testing  road  stone,  181-187 

— ,  — ,  absorption,  187 

— ,  —      — ,  cementing      value, 
definition,  184 

— , ,  compression,  187 

— ,  -        — ,  durability,  187 
— ,  —        — ,  hardness  test,  181 
— ,  —        — ,  resistance  to  wear, 

185 

— ,  —        — ,  specific  gravity,  186 
, ,  toughness,     defini- 
tion, 183 


370 


INDEX 


Bryan,  E.  U.,  72 

Bubble,  65 

Burned  clay  roads,  84 


Cast-iron  culverts,  107 

Cement,  bituminous,  specifications 

for,  302 
—  pipe,  109 
Chainman,  head,  36 

—  rear,  37 

Charts,  organization,  350-354 
Chase,,  Professor  L.  W.,  2,  362 
Cinder  roads, '85 
Clayed  roads,  162 
Clearing  right  of  way,  126 
Coal  slack  roads,  85 
Collimation,  line  of,  63,  64,  65 
Comparison  of  roads,  table  of.  86 
Concrete  box  culverts,  112 

—  culvert,  method  of  constructing, 

113-121 

slab,  table  of,  reinforcement, 

117 

—  culverts,  Minnesota,  table  of ,  121 

—  foundations,  206 

,  aggregate,  209 

,  hand  mixing,  207 

,  machine  mixing,  208 

— ,  measuring  aggregates,  207 
-  roads,  83,  233-288 

',  aggregates,  235-247 

,  — ,  coarse,  238 

,  — ,  equations  for  proportion- 
ing, 243-248 

,  — ,  error  in  proportioning  by 

voids,  240 

,  — ,  fine,  235 

,  — ,  graded  sand,  237 

,  — ,  maximum  density  curve, 

to  construct,  241 

,  — ,  proportioning,  239 

,  — ,  —  by  arbitrary  selection, 

239 


Concrete  roads,  aggregates,  propor- 
tioning by  maximum 
density  curves,  241 
— ,  — ,  —  by  voids,  239 

,  — ,  — ,  mathematical  analysis, 

242-248 

!  -    — ,  — ,  —  very  fine,  261 
— ,  — ,  reinforcement,  238 

,  — ,  water,  238 

— ,  automatic  measuring  devices, 

268 

— ,  automobiles,  effect  of,  on,  233 
— ,  bituminous,  306-313 
— ,  consistency  of  concrete,  269 
— ,  cost  of,  284,  285 
— ,  cross-section,  282 
— ,  crown  or  slope,  283 
•  — ,  curing  and  protecting,  277 
— ,  cylinder  slump,  270 

,  design  of  concrete  mixtures, 

254 

,  Edwards'  surf  ace  area  method 

of  concrete  proportions,  260 

,  expansion    and    contraction 

joints,  279 
— ,  finishing,  275,  276 

,  forms,  275 

— ,  grouting,  286 

— ,  Hassam  pavement,  286 

— ,  integral  curb,  283 

— ,  joining  straightedge,  275 

— ,  joint-protection  plates,  279 

— ,  maintenance,  283 

— ,  materials,  233-235 

— ,  — ,  cement,  233 

— ,  — ,  handling,  287,  288 

,  — ,  quantities  of,  Fuller's  rule, 

261-264 

,  — ,  specifications,  234 

— ,  measuring  the  materials,  267 

,  mixers,  264 

— ,  —  gravity,  267 

,  — ,  paddle,  266 

,  — ,  rotary,  266- 


INDEX 


371 


Concrete   roads,  mixers,   selecting, 

287 
— ,  mixing,  duration  and  speed, 

272 

— ,  oil-cement  concrete,  286 
— ,  organization,  286-288 
— ,  — ,  preliminary  planning,  286 

,  placing  concrete,  274 

,  ponding    method  of    curing, 

278 

— ,  proportions  for  concrete  mix- 
ing, table  of,  256,  257 
— ,  —  used  in  practice,  248-264 

, ,  Abrams'  fineness 

modulus  meth- 
od, 249 

, • ,  fineness  modu- 
lus determina- 
tion, 251 

, ,  maximum  per- 
missible values 
of  fineness  mod- 
ulus, '253 

,  protection  from  freezing,  278 

— ,  reinforcing,   277 
— ,  repairs,  284 
— ,  seal  coat  or  carpet,  284 
— ,  slump   test  for  consistency, 
270,  271 

' ,  specific  gravity  of  aggregates, 

table  of,  263 

1 ,  striking  off  templates,  274 

,  truncated  cone  slump,  270 

' ,  two-course  work,  278 

,  water,   quantity  required  in 

mixing  concrete,  table  of, 
258,  271 

,  weighing  devices,  268 

— ,  width,  282 
Corduroy  roads,  85 
Corrugated  iron  and  steel  plate  cul- 
verts, 107  . 

Cost  maintenance  of  various  types 
of  road,  15,  16 


Cost  of  concrete  roads,  284,  285 
—  sand  clay  roads,  164-166 
County  and  township  organization, 

350-355 
Crown,  73 
—  corrections,  49 
— ,  table  of,  50 

Cross-section  notes,  recording,  69 
Cross-sectioning,  65-69 
Culverts  and  bridges,  103-122 

— ,  concrete,  construction  of, 
113-121 

,  — ,  —  — ,  arch    culverts, 

116 

— ,  — , ,  deposition      o  f 

concrete,  114 
— ,  — ,  -  — ,  forms,  119 

— ,  — , ,  guard  rails  and 

parapets,    120 

— ,  — ,  —  — ,  head  and  wing 
walls,  115 

,  — ,  —  — ,    removal        o  f 

forms,        115, 
119 

— ,  — , ,  slab-bridges, 

115 

— ,  — , ,    wooden  forms, 

113 

— ,  definition,  103 
— ,  design,  104 
— ,  fords,  122   . 
— ,  permanent  structures,  107- 

112 
— ,  —  — ,  box  culverts,  111 

— , ,  cast-iron,  107 

— ,  —  — ,  cement  pipe,  109 
— ,  • ,  concrete    box    cul- 
verts, 112 

— ,  —  — ,  corrugated  iron  and 
steel  plate,  107 

— , ,  end       protection, 

110 

, ,  foundation,  110 

, ,  intake  drop,  110 


372 


INDEX 


Culverts  and  bridges,  concrete,  per- 
manent struc- 
tures, twin-  pipe 
culvert,  110 

, ,  vitrified   clay  'pipe, 

109 

,  size  of  waterway,  103 

,  temporary  structures,  105- 

107 

— ,  —  — ,  high   -   water   low 
bridge,  105 

— , ,  pile    and    stringer 

bridge,  106 

— ,  —  — ,  piling,  bearing  pow- 
er of,  106 

, ,  wooden  box  cul- 
verts, 105 

Cumberland  road,  342 

Curve,  laying  out,  55-62 

— ,  locating  by  eye,  60 

— ,  striking  in  the,  60 

—  to  locate  by  chord  offsets,  58 

—  to    locate    by   tangent    offsets, 

59 

Curves,  52,  53 
— ,  formulas  for,  52-54 
— ,  parabolic,  60 
— ,  slight  effect  of,  on  length  of  road, 

20 
— ,  vertical,  61,  62 


Detour  signs,  304 

Deval  abrasion  machine,  185 

Development  of  road  systems,  340- 

344 

Ditches,  deep  side,  92 
Dodge,  General,  84 
Dorry  test  for  hardness,  182 
Draftsman,  43 
Drag  or  slip  scraper,  134 
— ,  use  of,  on  earth  roads,  142-147 
Drain,  blind,  93 
—  tile,  93-97 


Drain,  tile,  size,  formulas  for,  94- 

97 

Drainage,  87-102,  124 
— ,  crown,  87 
— ,  — ,  formula  for,  88 

—  of  earth  roads,  124 

—  gravel  roads,  175 
— ,  side  ditches,  89-91 
— ,  sub-drainage,  92-102 
— ,  — ,  deep  side  ditches,  92 
— ,  — ,  drain  tile,  93-97 
— ,  — ,  filling  ditch,  99 
— ,  — ,  laying  tile  for,  97-99 
— ,  — ,  number  of  acres  drained  by 

tiles,  table  of,  96 
— ,  — ,  outlets  in  tile,  100 
— ,  — ,  ponds,  101 
— ,  — ,  V-drains,  100 
— ,  — ,  water  courses,  101 
Draining  ponds,  101 
Dump  boards,  137 

—  wagons,  137 

Dust,  cause  of,  322-324 

— ,  palliatives  and  preventives,  324- 

328 
— ,  — ,  annual   and   vegetable  oils, 

328 

— ,  — ,  deliquescent  salts,  325 
— ,  — ,  emulsions,  326 
— ,  — ,  light  oils,  327 
— ,  — ^  oil^and  water,  325 
— ,  — ,  organic  substances,  326 
— ,  — ,  water,  325 
— ,  — ,  sea  water,  325 
— ,  — ,  tars,  328 

— ,  preventives,  bituminous  surf  aces, 
329-332 

— ,  — , ,  construction,  331 

— ,  — ,  —  — ,  materials,  329 

— ,  — , ,  oil,  332 

— ,  — , ,  oiled  roads,  329 

— ,  — , ,  specifications,  329 

— ,-  surface  treatments  to  mitigate 
and  prevent,  322-332 


INDEX 


373 


E 

Earth  roads,  80,  123-149 

,  alignment  and  grades,  125 

,  clay,  definition,  123 

— ,  clearing  right  of  way,  126 
,  drainage,  124 

— ,  grading,  130-141 

— ,  — ,  blade  grader,  130-132 

,  — ,  borrow  pits,  140 

,  — ,  drag  or  slip  scraper,  134 

,  — ,  dump  boards,  137 

— ,  — ,  —  wagons,  137 

— , ,  embankment,  140 

,  — ,  elevating  grader,  138 

,  — ,  Fresno  or  buck   scraper, 

136 

,  — ,  harrow,  132 

,  — ,  haul  and  overhaul,  140 

,  — ,  machines  and  tools,  130 

— ,  — ,  plow,  133 
,  — ,  shrinkage,  140 

— ,  — ,  spades  and  shovels,  139 

,  — ,  steam  shovels,   drag  line 

scrapers     and     indus- 
trial railways,  139 

— ,  — ,  tongue   or   pole   scraper, 
135 

—  — ,  — ,  tractors  vs.  horses,  141 

,  — ,  wheel  scrapers,  136 

,  maintenance  of,  141-149 

,  — ,  drag,  method  of  using,  145 

,  — ,  — ,  theory  and  use  of,  143 

,  — ,  dragging,  142-147 

,  — ,  — ,  rules  for,  146 

— ,  —  drags,  142 
,  — .  patrol  system,  147-149 

—  — ,  — ,  Pennsylvania  State  rules 

for,  147-149 

,  sand,  definition,  123 

,  staking  out,  126 

,  varieties  of  earth,  123 

,  width  of,  125 

,  —  and  cross-section  of  road- 
way, 127-130 


Earthwork  computation,  tables  of, 

47,48 
Economic  advantages  of  good  roads, 

2-7 

Edgren,  A.  H.,  316 
Edwards,  L.  N.,  260 
Elevating  grader,  138 
Expansion  and  contraction  points, 

279 

F 
Farm  trucks  and  motor  transport, 

13 

Field  procedure,  77 
Flagman,  front,  28 
— ,  rear,  38 
Fords,  122 
Fore  sight,  39 

Fresno  or  buck  scraper,  136 
Fuller,  W.  B.,  171 
Furnace  slag  road,  85 

G 

Gillespie,  quoted,  20 

Grade  line,  establishing,  46-50 

— ,  minimum,  30 

-  point,  66 

—  status,  66,  67 
Grades,  definition,  21 

—  or  gradient,  defined,  33 
Grading  earth  roads,  130-141 

— ,  gravel  roads,  plotting  standard, 

173 

—  machines  and  tools,  130 
Gravel,  composition  of,  167 

-  roads,  82,  167-180 

,  American  Society  of  Muni- 
cipal Improvements  speci- 
fications, 112 

,  binding  action  of  gravel.  174 

,  calibrating  sieves,  169 

,  chemical  tests  of  gravel,  174 

,  Colorado  specifications,  172 

,  construction,  175-178 

,  — ,  chert  or  flint,  177 


374 


INDEX 


Gravel     roads,      construction     of, 
design,  175 

,  — ,  drainage,  175 

,  — ,  spike-tooth   harrow,  176, 

note 

— ,  — ,  surface  method,  176 
— ,  — ,  trench  method,  177 
— ,  density  of  gravel,  169 

— ,  grading  gravel,  table  of,  170 
— ,  — ,  plotting    standard,     173, 

174 

— ,  — ,  refinement  in,  171 
— ,  mechanical   analyses    curves 

defined,  168 

— ,  Missouri  specifications,  172 
— ,  New    Jersey    specifications, 

171 
— ,  repairs  and  maintenance,  179, 

180 

— ,  sieves,  168 
Guard  rails,  91 
and  parapets,  120 


Hassam  pavement.  286 
Haul  and  overhaul,  140 
Haulage,  amount  of,  8-15 
— r  estimating  by  traffic  area,  8 

— , census,  8 

— ,  motor  truck,  cost  of,  7 

Hauling,  cost  of,  2,  6 

Hay  roads,  85 

Highway  departments,  duties  of,  348 

High-water  low  bridge,  105 


Intermediate  sights,  40 
Investment,  economic,  12,  13 


James,  E.  W.,  12 

James'  test  of  sand-clay  mixtures, 

160 
Johnson,  A.  N.,  256,  285 


K 

King,  D.  Ward,  142 

Koch,  Professor,  analysis  of  sand, 

153 
Koch's  method  of  testing  sand-clay 

mixtures,  159 


Lancaster  turnpike,  342 

Laws,    typical,    for    formation    of 

highway  departments,  348 
Lajdng  out  a  new  road,  31-33 
Level  and  transit,  adjustments  of, 

62-65 

—  board,  use  of,  66 

— ,  dumpy,  adjustments  of,  65 

-  party,  39 

—  viol,  64 

-  Y,  adjustments  of,  64 
Leveling,  66 

Load  a  tractor  can  pull  upgrade,  27 
Lord,  Edwin  C.  E.,  187 

M 

Macadam,  automobile,  effect  of  on, 

199 
Macadam,  John  London,  191,  note. 

-  roads,  82 

—  — ,  bituminous,  300,  301 

-  defined,  191 

Me  Math  formula  for  area  of  water- 
way, 104 
Maintenance  competition,  362 

,  local  superintendents,  rating, 

362 

—  costs  of  good  roads,  15,  16 

—  of  concrete  roads,  283  . 
—  of  bituminous  roads,  306 

—  of  broken-stone  road,  198-200 

—  of  earth  roads,  141-149 
Minimum  grade,  30 
Mixers,  concrete,  264 

— ,  — ,  gravity,  267 
— ,  — ,  paddle,  266 


INDEX 


375 


Mixers,  concrete,  rotary,  265 
Monolithic  brick  pavement,  222- 

224 

Moorefield,  C.  H.,  286 
Motor  transport  for  farmers,  13 
—  track  cost  per  day,  7 

O 

Obstacles,  how  crossed,  31 
Office  work,  77 
Organization,  county  and  township, 

350-355 

— ,  -        — ,  charts,  351-354 
Overhead   charges,    effect   of   good 
roads  on,  4 


Palliatives  and  preventives  of  dust, 

324-328 
Patrol  system  of  road  maintenance, 

147-149 

Pavement  foundations,  202-210 
— ,  definition,  202 
— ,  foundations  proper,  205-210 
— ,  —  — ,  aggregate,  208, 

— , ,  brick,  210 

— , ,  concrete  manufactured 

in  place,  210 

— ,  —  — ,  proportioning,  206 
— ,  —  — ,  hand  mixing,  207 
— , ,  hydraulic  cement  con- 
crete, 206 

, ,  macadam,  206 

— ,  —  — ,  machine  mixing,  208 
— ,  —  — ,  measuring  aggregates, 

207 
— ,  —  — ,  Missouri,  205 

— , ,  placing,  208 

, ,  protection  during  hard- 
ening, 208 

, ,  telford,  205 

, ,  V-drain,  206 

,  safe  bearing  loads,  203 


Pavement  foundations,  strengthen- 
ing the  subgrade,  205 
— ,  subgrade,  203 
Pile  and  stringer  bridge,  106 
Piling,   bearing  power  of,  formula 

for,  106 

Plank  roads,  85 
Plate  bubble,  63 
Ponds,  draining,  101 
Preliminary  survey,  31,  32 
Primary  transportation,  5 
Profile,  45 
Pull,   needed  on  various  types  of 

road,  table  of,  23 

Q 

Quantities,  calculating,  70-73 

R 

Race  tracks,  362-365 
Rattler  test  of  paving  brick,  214 
Reconnoissance,  31 
Reinforced  concrete  floor  slab  di- 
mensions, 113 
Relocating  road  along  existing  lines, 

75 
— ,  cost  of,  29 

,  estimating  cost  of,  21 

— ,  party  for,  76 

Revenue,  administration,  and  organ- 
ization, 333-355 

^ 

— ,  — , ,  annuity  bonds,   337- 

339 

— ,  — , ,  licenses,  340 

— ,  — , ,  bonds,  334 

— ,  —  — ,  — ,  comparison   of   serial 

and  annuity  bonds, 

339 

— , ,  — ,  general  taxes,  334 

— , ,  — ,  indirect  taxation,  334 

— , ,  — ,  labor  taxes,  334 

— , ,  — ,  serial  bonds,  336,  337 

— ,  — ,  —  — ,  sinking-fund,  335 
— ,  — ,  —  — ,  special  taxes,  333 
— i  — , ,  taxes,  333 


376 


INDEX 


Rise  and  fall,  definition,  28 
Roads,  concrete,  233-288 
Road  location,  19-78 

—  an  engineering  problem,  19 

,  blade  grader  work,  74 

,  borrow  pits,  75 

,  cross-sectioning,  65—69 

,  — •  — ,  grade  point,  66 

, ,  —  stake,  66,  67 

, ,  leveling,  66 

,  —    —  notes,  recording,  69 

, ,  slope  stakes,  66 

, ,  stakes,  setting,  67,  68 

,  crown,  73 

,  curves,  52,  53 

,  existing  layouts,  75-78 

,  —  — ,  field  procedure,  77 

,  —  — ,  office  work,  77 

— ,  —  — ,  relocations,  75 

, ,  stadia  surveying,  78 

— ,  —  — ,  surveying    operations, 
•     76 

,  formulas  for,  52-54 

— ,  general  principles,  20-31 

,  —  — ,  directness,  20 

, ,  grades,  definition,  21 

, ,  —  formulas  for,  22 

, ,  obstacles,  how  crossed, ' 

31 

-,  —  — ,  pull  required  on  vari- 
ous types  of  road, 
23 

, ,  relocating  road,  esti- 
mating cost,  21 

,  —  — ,  relocation,  cost  of,  29 

, ,  rise  and  fall,  definition, 

28 

, ,  tractive  resistance  due 

to  grades,  tables  of, 
25 

,  grade  line,  earthwork  com- 
putation, tables  of, 
46,47 
, ,  establishing,  46-50 


Road  location,   grade   line,  crown 
corrections,    49;     table    of, 
50 
— ,  laying  out,  31-33 

— , curve,  55-62 

— ,  —     -  — -,  form  of  transit  notes, 

57 
— ,  —        — ,  parabolic,  60 

, — ,  striking  in,  60 

— , — ,  locating   by   chord 

offsets,  58 

— , ,  —  eye,  60 

— ,  —    —  • — ,  —  tangent  offsets, 

59 

— ,  -        — ,  vertical,  61,  62 
— ,  —        — ,  with    transit    and 

tape,  55,  56 
— ,  —  — ,  grades   and    gradient, 

33 

— ,  —  — ,  minimum  grade,  30 
— ,  —  — ,  party  organization,  34 

— , ,  preliminary  survey,  31, 

32 

,  —  — ,  reconnoissance,  31 

— , ,  stakes,  33 

— ,  -? ,  stationing,  32 

— ,  line  of  selected  route,  51 

— ,  party  for  relocation  work,  76 

— ,  preliminary  traverse,  34-45 

— ,  —  — ,  axman,  38 

— ,  —  — ,  draftsman,  43,  44 

— ,  —  — ,  flagman,  front,  38 

— , ,  — ,  rear,  38 

, ,  head  chaihman,  30 

— ,  —  — ,  level  party,  39 

— , ,  operation,   34-36,   40, 

41 

— ,  —  — ,  profile.  45 
— ,  —  — ,  rear  chainman,  37 

,  —  — ,  rodman,  41 

— , ,  stakeman,  37 

— ,  —  — ,  topographer,  42 
— ,  —  — ,  topographical  map,  46 
, ,  transit  man,  34 


INDEX 


377 


Road  location,  quantities,  calculat- 
ing, 70-73 

,  settlement,  74 

— ,  shrinkage,  74 

,  transit  and  level,  62-65 

, — ,  dumpy    level    ad- 
justments, 65 

, ,     transit,       adjust- 
ments of,  62,  64 

, ,     Y-level      adjust- 
ments, 64 

— ,  wasted  earth,  75 

—  maintenance    competition,    362 
,  local  superintendents,  rat- 
ing, 362 

—  signs  and  emblems,  356-361 

,  detour  signs,  360 

,  placing,  361 

Roads,  asphalt  block,  83 

— ,  bituminized  earth,  298,  299 
— ,  bituminous,  289-321 
— -,  —  macadam,  82 

—  brick,  83,  21 1-225 

— ,  broken-stone,  181-201 
— ,  burned  clay,  84 
— ,  cinder,  85 
— ,  coal  slack,  85 
— ,  comparison  of,  table  of,  86 
— ,  concrete,  83 

— ,  considerations  in  selecting  type 
of,  79 

—  corduroy,  85 

— ,  earth,  80,  123-149 

— ,  — ,  cost  of  construction  of,  80 

— ,  — ,  good  and  bad  qualities  of, 

81 

— ,  furnace  slag,  85 
— ,  good,  as  profitable  business  prop- 
osition, 16,  17,  18 
— ,  — ,    economic    advantages    of, 

2-7 

— ,  — ,  effects  of  on  marketing,  3 
— ,  — , town  business  man, 

3,17 


Roads,    good,    maintenance    costs, 

15,  16 

— ,  — ,  reduce  overhead  charges,  4 
— ,  — ,  social  advantages  of,  2 
— ,  gravel,  82,  167-180 
— ,  hay,  85 
— ,  macadam,  82 
— ,  plank,  85 
— ,  sand-clay,  81 
— ,  —  and  top-soil,  150-166 
— ,  shell,  84 
— ,  sheet  asphalt,  83 
— ,  stone  block  pavement,  225-228 
— ,  types  and  adaptations  of,  79-86 
— ,  wheelways,  84 
— ,  wood  block,  228-232 
Rocks,  classification  of,  187,  188 
Rodman,  41 
Roman,  F.  L.,  270,  271 


Safe  bearing  loads,  203 

Sand-clay  roads,  81 

—  and  top-soil  roads,  150-166 

,  clayed  roads,  162 

— ,  construction  of,  161 
— ,  cost,  164-166 
— ,  floui  ing  test,  161 
— ,  James'  field  testof  sand- 
clay  mixtures,  160 
— ,  Koch's    test    of    mix- 
tures, 159 

,  maintenance,    164-166 

,  materials,  selection  of, 

152-161 

,  —       — ,  A.  S.  T.  M. 

specification, 
154 

, ,mechanical 

analysis    of 
sand,  153 

, ,  separation  of 

sand     and 
clay,  152 


378 


INDEX 


Sand-clay  and  top-soil  roads,  ma- 
terials, selection  of, 
standard  sand-clay 
mixtures,  153 

,  proportioning,  method 

of,  156-158 

,  sanded  roads,  161 

,  sieve  analyses,  plotting, 

155-159 

,  test  for  mica  and  feld- 
spar, 161 
— ,  theory  of,  150-151 

,  top-soil  roads,  163 

—  mixtures,  standard,  153-154 
Sand,  mechanical  analysis  of,  153 
Sanded  roads,  161 
Secondary  transportation,  5 
Serial  bonds  for  road  construction, 

336,  337 
Settlement,  74 
Shales,  211,  212 
Shell  roads,  84 

Sheet  asphalt  roads,  83,  314-321 
Shrinkage,  74 
Side  ditches,  89-91 
Sieve  analyses,  straight-line  method 

of  plotting,  155-159 
Sieves  gravel,  169 
— ,  — ,  calibrating,  169 
Signs  and  emblems,  road,  356-361 
Simple  curve  formulas,  54 
Sinking-fund  for  road  construction, 

equations  for,  335,  336 
Slope  stakes,  66 

Slump  test  for  consistency  of  con- 
crete, 270,  271 

Spalding's  table  of  tile  drain  capac- 
ity, 95 

Spoon,  W.  L.,  161,  164 
Stadia  surveying,  78 
Standard   culvert   slabs,    reinforce- 
ment of,  table  of,  117 
Stakeman,  37 
Stakes,  setting,  67,  68 


Staking  out  roads,  126 

Standards,  63 

State  highway  departments,  346 

-  laws,  347-350 
Stationing,  32 

Steel  plate  and  corrugated  iron  cul- 
verts, 107 
Stone  block  pavements,  225-228 

,  construction,  227 

— ,  materials  used,  varieties  of, 

226 

— ,  physical  properties,  226 
— ,  size  of  blocks,  225 
— ,  small  and  recut  blocks,  228 
— ,  specifications,  227 

—  crushers  and  screens,  200,  201 
— ,  testing  road,  181-187 
Sub-drainage,  92-102 

Subgrade  of  pavement  foundations, 

203 

— ,  strengthening  the,  205 
Surface  drainage,  87-91 

—  treatments  to  mitigate  and  pre- 

vent dust,  322-332 


Talbot's  formula  for  area  of  water- 
way, 104 

Tar  melting-point  test,  295 

Telford,  Thomas,  84,  190,  note 

Telford  road  defined,  191 

Thompson,  S.  E.,  171 

Tile,  laying,  97-99 

— ,  outlets  in  drain,  100 

— ,  size  of  drain,  94 

Tiles,  number  of  acres  drained  by, 
table  of,  96 

Tongue  or  pole  scraper,  135 

Tonkel,  W.  G.,  362 

Tonnage,  formulas  for  ascertaining, 
10 

— ,  theoretical  average,  on  each  of 
six  market  roads,  table  of,  11 

Topographer,  42 


INDEX 


379 


Topographical  map,  46 

Top-soil  roads,  163 

Tractive  resistance  due  to  grades, 
tables  of,  25 

,  formulas  for  ascertaining,  26 

Tractor  load,  formula  for  ascertain- 
ing, 27 

Traffic,  analysis  of  distribution  of, 
12 

—  area,  estimating  haulage  by,  8 

—  census,  estimating  haulage  by,  8 

—  record  of  seven  improved  roads, 

table  of,  9 
Transit  man,  34 

—  operation,  34 

-  and  level,  adjustments  of,  62-65 
-  tape,  55,  56 

—  notes  for  curves,  form  of,  57 
Transportation,  primary,  5 

— ,  secondary,  5 

Traverse  survey,  methods  of  plat- 
ting, 44 

Tresaguet,  Pierre-Marie,  191,  note 

Turning  point,  39 

Twin  pipe  culvert,  110 

Types  and  adaptation  of  roads, 
79-86 


V-drains,  100,  206 


Vitrified  clay  pipe,  109 
Voshell,  J.  T.,  286 

W 

Wasted  earth,  75 

Water  courses,  how  drained,  101 

Waterway  in  culverts,  size  of,  103 

Weighing  devices  for  concrete  ma- 
terials, 268 

Wheel  scrapers,  136 

Wheelways,  84 

Whinery,  S.,  quoted,  42 

Width  and  cross-section  of  roadway, 
127-130 

Wood  block  pavements,  228-232 

,  bituminous  blocks,  231 

,  expansion  joints,  231 

— ,  filling,  230 

,  laying,  230 

,  preparation,  229 

,  tests,  .230 

,  treatment,  229 

,  varieties   of   wood    used, 

228 

Wooden  box  culverts,  105 


Y-level,  adjustments  of,  64 
Young,  R.  B.,  260 
Y'B,  the,  64 


sJ<l   /    / 


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